ff 


Edmund  O'Wei, 


ORGANIC    CHEMISTRY 


LESSONS 


IN 


ORGANIC   CHEMISTRY 


PART   I.  — ELEMENTARY 


G.  S.  TURPIN,  M.A.  (CAMB.),  D.Sc.  (LOND.) 

PRINCIPAL   OF  THE  TECHNICAL   SCHOOL,   HUDDERSFIELD 


gorfe 
MACMILLAN    AND    CO. 

AND     LONDON 
1894 

All  rights  reserved 


COPYRIGHT,  1894, 
BY  MACMILLAN   AND  CO. 

INMEMQR1AW 


Xortoooti 
Berwick  &  Smith,   Boston,  U.S.A. 


CONTENTS 


ELEMENTARY 

CHAP.  PAGE 

1.  THE  ANALYSIS  OF  ORGANIC  BODIES  .                                i 

2.  EMPIRICAL  AND  MOLECULAR  FORMULAE  .  .  .12 

3.  HYDROCARBONS  OF  THE  METHANE  SERIES  .       19 

4.  OLEFINES  AND  ACETYLENE.            .  .  .  .28 

5.  HALOID  DERIVATIVES          .  37 

6.  THE  ALCOHOLS         .            .            .  .  .  -44 

7.  ETHEREAL  SALTS — Ethers — Mercaptan  .  .  -55 

8.  ALDEHYDES  AND  KETONES  .            .  .  .  .61 

9.  THE  FATTY  ACIDS  .            .            .  .  .  .68 

10.  ACETYL  CHLORIDE  AND  ACETIC  ANHYDRIDE       .  .       79 

11.  THE  AMINES  .  .  .  .  .  .82 

12.  THE  AMIDES  AND  AMIDO- ACIDS    .  .  .  .88 

13.  ALKYL  COMPOUNDS  OF  PHOSPHORUS,  ARSENIC,  SILICON, 

AND  THE  METALS  .  .  .  .  .92 

14.  GLYCOL  AND  ITS  DERIVATIVES.     SUCCINIC,  MALIC,  AND 

TARTARIC  ACIDS  .  ....      99 


889773 


ORGANIC  CHEMISTRY 


CHAP.  PAGE 

15.  LACTIC  AND  CITRIC  ACIDS.  .  .  .     106 

16.  THE  ALLYL  COMPOUNDS      .  no 

17.  GLYCERINE  AND  ITS  COMPOUNDS  .  .             .  .      115 

1 8.  THE  CARBOHYDRATES           .  .  .            .  .119 

19.  UREA  AND  URIC  ACID         .....     128 

20.  THE  CYANOGEN  COMPOUNDS  .  .            .  .131 


ELEMENTARY 

CHAPTER    I 
THE  ANALYSIS  OF  ORGANIC  BODIES 

Province  of  Organic  Chemistry. — L/p>  r£  the  beginning 
of  this  century  it  was  gcnei'aiiy  supposed  ajhat  all  chemical 
substances  might  be  sharply divided' intQ  tvrc'cksses,  according 
as  their  formation  was,'  pr.'w&s  ri.ojt,;  pds,s:.il)l?;  tyir'.htW.the  aid  of 
living  organisms  ;  those  compounds  which  had  been  obtained 
only  from  some  animal  or  plant  were  called  organic  bodies, 
and  the  action  of  the  mysterious  "vital  force"  was  believed 
to  be  necessary  for  their  formation.  In  1828,  however,  the 
German  chemist  Wohler  prepared  urea,  a  typical  organic 
substance,  from  inorganic  materials  by  a  chemical  reaction  of 
very  simple  character,  and  thus  broke  down  the  separation 
which  up  to  that  time  had  been  maintained  between  inorganic 
and  organic  substances  ;  but,  as  a  matter  of  convenience,  we 
still  retain  the  name  organic  chemistry  for  a  department  of  the 
science  which  is  concerned  with  the  chemistry  of  the  com- 
pounds of  two  elements,  carbon  and  hydrogen,  and  their 
numerous  derivatives.  Amongst  these  are  included  nearly  all 
the  substances  formed  by  the  complicated  chemical  processes 
lying  at  the  base  of  life,  whether  animal  or  vegetable,  as  well 
as  a  still  larger  number  which  have  been  prepared  artificially 
by  the  simple  processes  of  the  laboratory.  Many  compounds 
obtained,  in  the  first  place,  from  animals  or  plants  have  been 

IE  B 


ORGANIC  CHEMISTRY 


afterwards  manufactured  in  the  laboratory,  and  chemists  have 
good  reason  to  believe  that  in  the  future  there  will  be  no 
single  substance  known  whose  formation  cannot  be  brought 
about  by  ordinary  chemical  reactions. 

The  distinction  betwreen  organic  and  inorganic  chemistry 
is,  then,  merely  a  convenient  division  of  the  vast  material  of 
the  science,  and  organic  chemistry  may  be  defined  as  the 
chemistry  of  the  hydrocarbons  and  their  derivatives. 

Reasons  for  the  separate  Study  of  Organic  Chem- 
istry. --  The  reasons  which  make  it  convenient  still  to 
maintain  an  artificial  separation  between  inorganic  and  organic 
chemistry  are  chiefly  the  immense  number  of  organic  com- 
pounds known  —  a  number  which  receives  additions  every- 
day— and  the  different  character  of  the  problems  presented  to 
us  by  them  as  compared  with  the  much  less  numerous  and 
comparatively  simple  inorganic  bodies.  In  organic  chemistry 
the  most  important  points  claiming  our  attention  are  the 
grouping  of  the  atoms  present  in  .each  compound,  and  the 
influence  of  th;is'  grouping*  on 'the 'properties  of  that  compound. 
We  shall  find  cases  'where  the  'molecules  of  two  different 
substances  .  c'oftta'in '  exactly  ;  sin>iU(r  atoms,  and  in  the  same 
number,  but  -trie  different  arrangement  -of  the  atoms  in  the  two 
molecules  produces  bodies  with  markedly  different  properties. 

The  name  isomerism  is  given  to  this  phenomenon.  Cases 
of  it  are  almost  unknown  in  inorganic  chemistry,  but  are 
extremely  frequent  in  organic  chemistry  ;  see  p.  24  for  a  further 
account  of  it. 

On  the  other  hand,  we  often  find  a  series  of  organic  com- 
pounds, all  of  different  composition,  but  possessing  very 
similar  properties,  owing  to  the  presence  in  their  molecules  of 
the  same  group  of  atoms  ;  prominent  instances  of  this  are 
furnished  by  the  homologous  series,  of  which  more  is  said 
on  p.  21. 

Elements  present  in  Organic  Compounds. — Every 
organic  compound  contains  carbon,  and  in  nearly  every  one 
hydrogen  is  also  found  ;  the  other  elements  may  any  of  them 
occur,  but  those  more  frequently  found  are  nitrogen,  oxygen,  the 
halogens,  sulphur,  and  phosphorus. 

The  carbon,  hydrogen,  and  nitrogen  are  most  satisfactorily 
detected  by  heating  the  substance  with  copper  oxide  in  a 


ORGANIC  ANALYSIS 


hard-glass  tube  ;  the  organic  material  is  burned  up  by  the 
oxygen  of  the  copper  oxide,  some  of  which  is  reduced  to 
metallic  copper,  and  the  products  of  the  combustion  are 
carbon  dioxide,  water,  and  nitrogen  gas.  If  no  water  is 
produced  by  the  combustion,  then  no  hydrogen  was  present  in 
the  substance  examined,  and  if  no  nitrogen  be  given  off,  that 
element  was  similarly  absent  from  the  material  employed. 

EXPT.  i.  Take  a  piece  of  ordinary  combustion  tubing  closed  at  one 
end  ;  introduce  into  it  (a)  enough  dry  cupric  oxide  (best  granulated)  to  fill 
about  three  inches  of  the  tube  ;  (b]  then  about  one  gram  of  sugar  ;  (c )  and 
lastly,  fill  the  tube  nearly  to  the  open  end  with  more  granulated  copper 
oxide.  Close  the  open  end  of  the  tube  with  a  well-fitting  rubber  stopper, 
through  which  passes  a  piece  of  glass  tubing  carrying  a  small  bulb,  and 
connect  this  with  two  small  wash-cylinders,  of  which  the  first  contains 
lime-water  (better,  baryta  water),  and  the  second  strong  solution  of 
caustic  soda. 


FIG.  i. — Apparatus  for  Experiments  i  and  2. 

Heat  the  tube  carefully  in  a  combustion  furnace,  or  over  a  row  of  four 
Bunsen  burners  ;  first  applying  heat  at  the  two  ends  of  the  tube,  and 
when  these  have  become  just  red-hot,  turning  up  gradually  the  two 
middle  burners.  Notice  the  production  of  water  and  CO2,  and  that  no 
nitrogen  escapes  from  the  second  wash-cylinder  after  the  air  has  been  all 
driven  out. 

EXPT.  2.  Repeat,  using  urea  instead  of  sugar.  Notice  the  large 
amount  of  gas  evolved  which  is  not  absorbed  by  the  caustic  soda.  Urea 
contains  nearly  fifty  per  cent  of  nitrogen. 


When  proper  precautions  are  applied  this  method  of 
combustion  with  copper  oxide  enables  us  to  determine  with 
considerable  accuracy  the  amounts  of  carbon,  hydrogen,  and 
nitrogen  present  in  any  organic  substance.  The  carbon  and 
hydrogen  are  usually  determined  by  one  experiment,  the 
nitrogen  by  a  second. 


ESTIMATION  OF  CHAP. 


Quantitative  Determination  of  Carbon  and  Hydro- 
gen.—  There  are  several  variations  in  the  details  of  the 
experiment  as  adopted  by  different  chemists  ;  we  shall  describe 
only  one  plan  of  work. 

A  piece  of  hard-glass  tubing,  long  enough  to  project  about 
an  inch  from  each  end  of  the  combustion  furnace,  is  connected 

at  the  one  end  with  a 
tube,    through    which 
or  oxygen— 
in  each   case  dry  and 

FIG.  2.— Flask  fitted  with  CaCl2  tube,  in  which  the  f  frrirn  ~ai.u™  rUr,v 
copper  oxide  is  allowed  to  cool  after  being  dried  tree  tr°m  Carbon  Q1OX- 
by  heating  to  redness.  ide may  be  Supplied 

at    will  ;    and    at    the 

other  end,  with  a  U  tube  containing  lumps  of  porous  CaCl9, 
to  absorb  and  retain  the  water  produced  in  the  combustion, 
followed  by  a  potash  apparatus  (Fig.  5),  which  similarly 
absorbs  the  carbon  dioxide. 

About  two-thirds  of  the  combustion  tube  at  the  end  nearer 
the  absorbing  tubes  is  filled  with  granulated  copper  oxide, 
kept  in  position  by  two  plugs  of  copper  gauze  ;  behind  this  is 
a  "  boat "  of  porcelain  or  platinum,  into  which  about  one-fifth 


FIG.  3. — Tube  arranged  for  combustion  in  a  current  of  Oxygen  ;  the  CaClo  tube 
only  is  shown  attached. 


of  a  gram  of  the  substance  to  be  analysed  has  been  accurately 
weighed  ;  and  then  follows  a  longer  plug  of  oxidised  copper 
gauze,  whose  object  is  to  prevent  any  backward  diffusion  of 
the  products  of  the  combustion. 

The  copper  oxide  having  been  previously  thoroughly  dried, 
the  portions  of  the  tube  on  either  side  of  the  boat  are  first 
raised  to  a  dull  red  heat,  and  the  actual  combustion  is  then 
begun  by  carefully  and  gradually  applying  heat  to  the 
substance  in  the  boat,  while  a  very  slow  current  of  pure  air  is 
passed  through  the  apparatus.  Towards  the  end  oxygen  is 
introduced  in  place  of  air,  with  the  object  of  burning  up  any 
carbonaceous  residue  that  may  have  been  left  in  or  about  the 


CARBON  AND  HYDROGEN 


boat,  and  then  air  is  again  passed,  in  order  to  sweep  along 
any  CO2  or  oxygen  that  may  be  in  the  tube  or  absorbing 
apparatus.  (Oxygen  is  heavier  than  air,  hence  the  need  of 
leaving  the  absorbing  apparatus  filled  with  air  at  the  end,  as 
at  the  beginning,  of  the  combustion.) 

The  CaCl2  tube  and  the  potash  apparatus  were,  of  course, 
weighed  before  the  combustion  was  commenced ;  they  are 
weighed  again  after  it  is  over,  and  the  increase  of  weight 


FIG.  4.— U-tube  filled  with  CaClo  for 
absorbing  the  water  produced  in  the 
combustion. 


FIG.  5. — Potash  apparatus  for 
absorbing  the  CO2- 


gives  the  amount  of  water  and  of  carbon  dioxide  produced  by 
burning  a  known  weight  of  the  substance.  An  example  will 
best  illustrate  how  the  percentage  of  carbon  and  of  hydrogen 
present  in  the  substance  may  be  calculated. 

Example.   0.2386  gram  of  a  substance  gave  0.4879  gram  CO2  and 
0.0870  gram  H2O. 

The  percentage  of  carbon  =  100  x  '- — —  x  —  =  55.76, 

.2300     n 


for  .4879  gram  COg  contains  .4879  x  —  gram  of  carbon. 

The  percentage  of  hydrogen  =  100  x       7    x  -  =  4.05. 

.2386     9 

Quantitative  Determination  of  Nitrogen.  —  There 
are  several  methods  in  use,  but  the  only  one  which  is  appli- 
cable to  all  organic  bodies  alike  is  that  of  Dumas,  in  which  the 
substance  is  burned  with  copper  oxide  in  an  atmosphere  of 
carbon  dioxide,  and  the  liberated  nitrogen  collected  over  a 
solution  of  caustic  potash  and  measured. 


ESTIMATION  OF 


CHAP. 


Fig.  6  represents  the  apparatus  used.  The  combustion  tube 
is  filled  with  (a)  a  six-inch  length  of  granulated  oxide  ;  (b}  a 
mixture  of  a  known  weight  of  the  substance  with  powdered 
copper  oxide  ;  (c)  six  or  eight  inches  of  granulated  oxide  ; 
(</)  a  spiral  of  copper  gauze.  It  is  connected  at  one  end 


FIG.  6. 


with  an  apparatus  for  evolving  carbon  dioxide,  from  which, 
first  of  all,  a  steady  stream  of  the  gas  is  passed  for  at  least 
half  an  hour,  until  the  air  is  entirely  driven  out  from  the 
tube.  During  this  time  the  granulated  oxide  on  either  side 
of  the  mixture  (b)  may  be  cautiously  heated.  When  the  air 
is  expelled  the  collecting  apparatus  is  filled  to  the  tap  with 


FIG.  7.  —  Apparatus 
for  evolving  a 
steady  stream  of 
CO2  by  the  action 
of  HC1  upon 
marble. 


FIG.  8. — Apparatus  in  which   the    Nitrogen 
is  collected  over  potash  solution. 


potash    solution   by   raising  the  bulb,   the   tap   is   closed,  and 
the  stream  of  CO2  stopped ;  the  copper  spiral  is  now  heated 


NITROGEN 


to  redness  and  the  combustion  proceeded  with.  At  the  end 
more  CO2  is  passed,  in  order  to  sweep  out  any  nitrogen  from 
the  tube  and  carry  it  into  the  measuring  apparatus. 

It  is  necessary  to  mix  the  substance  with  powdered  CuO, 
as  otherwise  the  combustion  would  not  be  complete  in  the 
atmosphere  of  CO2.  The  object  of  the  copper  spiral  is  to 
reduce  any  oxides  of  nitrogen  that  might  be  evolved,  and  one 
must  also  be  used  in  determining  the  carbon  and  hydrogen  in 
a  nitrogenous  body. 

An  example  will  illustrate  the  method  of  calculation.  The 
work  is  much  simplified  by  the  use  of  tables  which  have  been 
specially  prepared  for  the  purpose. 

Example.  0.2258  gram  gave  28.3  c.c.  moist  nitrogen,  measured  at 
9.5°  C.  and  765.5  mm. 

The  only  difficulty  is  in  calculating  the  exact  weight  of  the  nitrogen. 
It  is  measured  over  strong  potash  solution,  whose  vapour  pressure  at 
9. 5°  C.  is  found  in  the  tables  as  7.  i  mm.  ;  the  pressure  of  the  nitrogen  is 
therefore  765.5  —  7.1  =  758.4  mm.  Its  volume  (measured  dry)  at  o°  and 
760  mm.  would  therefore  be 

758.4      273 

28. 3  x  1-2-IZ x     /J   =  27. 3  c.c. 
760      282.5 

and  its  weight  27. 3  x  .0000896  x  14  =  .03424  gram  (i  litre  H  weighs 
.0896  gram  at  normal  temperature  and  pressure).  The  percentage  of 

.03424  x 100 
nitrogen  is  therefore  — =15.16. 

Many  organic  bodies  containing  nitrogen  evolve  ammonia 
when  heated  with  soda  lime  (some,  however,  give  off  only 
part,  and  others  none,  of  their  nitrogen  in  the  shape  of 
ammonia),  and  on  this  plan  it  is  possible  in  many  cases  to 
detect  the  presence  of  nitrogen,  and  estimate  its  amount.  In 
the  quantitative  process  (known  by  the  names  of  Will  and 
Varrentrapp)  the  liberated  ammonia  is  absorbed  by  means  of 
dilute  hydrochloric  acid  placed  in  a  bulb  tube  of  suitable 
construction.  The  amount  of  the  ammonia  is  ascertained  by 
estimating  how  much  hydrochloric  acid  has  been  neutralised 
by  it. 

This  method  has  fallen  into  disuse,  having  been  replaced 
by  one  due  to  Kjeldahl,  which  is  applicable  in  all  cases  where 
Will  and  Varrentrapp's  can  be  used,  and  is  much  more 


8  ESTIMATION  OF  CHAP. 

convenient.  Kjeldahl  decomposes  the  substance  by  heating  it 
with  concentrated  sulphuric  acid  and  addition  of  a  little 
potassium  permanganate.  Under  this  treatment  the  nitrogen 
of  the  organic  body  is  in  many  cases  converted  into  ammonia, 
which  is  afterwards  liberated  by  addition  of  caustic  soda, 
distilled  off  and  collected  in  a  -measured  volume  of  dilute  acid 
of  standard  strength.  The  calculation  is  precisely  similar, 
whether  Will's  or  Kjeldahl's  method  be  adopted. 


FIG.  9. — One  form  of  apparatus  for  the  second  part  of  Kjeldahl's  process  ;  the 
ammonia  is  boiled  off  and  absorbed  by  standard  acid. 

Example.  1.2350  gram  of  a  substance  was  treated  by  Kjeldahl's 
method,  and  the  ammonia  produced  collected  in  25  c.  c.  of  dilute  hydro- 
chloric acid  of  normal  strength  ;  at  the  end  of  the  distillation  it  was  found 
that  15.3  c.c.  of  normal  soda  solution  were  needed  to  neutralise  the  excess 
of  acid  which  still  remained  uncombined. 

The  amount  of  ammonia  produced  was,  therefore,  sufficient  to 
neutralise  9.7  c.c.  (  =  25-15.3)  of  normal  acid;  that  is  to  say,  it  was 
equal  to  the  amount  contained  in  9.7  c.c.  of  a  normal  solution  of 
ammonia.  Such  a  solution  contains  17  grams  of  NH3  (molecular  weight 
=  17)  in  a  litre,  and  in  9.7  c.c.  there  would  be  17  x  9. 7  milligrams  NH3  ; 
of  this  14x9.7  mgms.  are  nitrogen,  and  therefore  the  percentage  of 

14  x .0097 

nitrogen  is    xi  00=11.0. 

1.2350 

Detection  and  Quantitative  Estimation  of  the 
Halogens. — Organic  substances  containing  chlorine,  bromine, 
or  iodine,  do  not,  as  a  rule,  react  at  all  readily  with  silver 


THE  HALOGENS 


nitrate  ;  it  is  necessary  first  to  decompose  the  organic  matter, 
for  which  purpose  either  of  the  two  following  methods  may 
be  used  : — 

(«)  Carius's  method  employs  nitric  acid  as  the  oxidising 
agent.  About  .2  gram  of  the  substance  is  intro- 
duced along  with  I  or  2  c.c.  of  fuming  nitric  acid 
and  a  crystal  of  silver  nitrate  into  a  tube  of  stout 
glass  ("  pressure  "  tubing  of  fairly  soft  glass  with 
walls  2  to  3  mm.  thick  is  the  most  convenient) 
about  40  cm.  long  and  2  cm.  external  diameter. 
The  open  end  of  the  tube  is  next  carefully  heated 
in  the  blow-pipe  flame  until  the  walls  have  thick- 
ened considerably  at  the  heated  spot,  and  then 
cautiously  drawn  out  into  a  thick-walled  capillary 
tube,  which  is  finally  sealed.  The  tube  so  prepared 
is  heated  in  a  specially  designed  and  very  strong 
air  bath  (or  "  cannon  ")  to  a  temperature  which 
varies,  according  to  the  character  of  the  substance 
to  be  analysed,  from  I  50°  to  300°  C.  for  one  or 
two  hours.  The  tube  must  be  allowed  to  cool 
inside  the  "cannon,"  and  even  when  cold  contains 
gases  (carbon  dioxide  and  oxides  of  nitrogen) 
under  such  considerable  pressure  that  its  opening 
can  only  be  safely  effected  by  heating  the  capillary 
tip  of  the  tube  in  a  flame  until  the  softened  glass  .. 

.r  FiG.io.-Sealed 

gives  way  before  the  internal  pressure,  and  allows  glass  tube 
the  compressed  gases  to  escape.  method™^ 

The    silver    chloride    (or    bromide    or    iodide)       analysis. 
formed  is  washed  out  from  the  tube  with  distilled 
water,   collected  on  a  filter,    washed,    dried   with  the    needful 
precautions  by  heating   to  fusion  in  a  porcelain  crucible,  and 
weighed. 

(£)  The  alternative  or  dry  method  consists  in  heating  the 
substance  with  pure  lime  in  a  combustion  tube  heated  in  an 
ordinary  combustion  furnace.  The  calcium  chloride  (or  bromide 
or  iodide)  produced  is  estimated  in  the  usual  way  by  precipita- 
tion with  silver  nitrate. 


Example.    (The   calculation   is   precisely  similar  in  both  cases.)    .1638 
gram  of  the  substance  yielded  .0953  gram  AgCl. 


ESTIMATION  OF 


CHAP. 


The  percentage  of  Cl  is  therefore,  since  145.4  Pai~ts  of  AgCl  contain 
37.4  of  chlorine, 

—  x  ioo 


The    detection 
accomplished    by 


.1638      145.4 
=  14.96. 

of    the    halogens 
applying    roughly 


FIG.  ii. — Air-bath  for  Carius's  method. 


can  most  certainly  be 
one  of  the  quantitative 
methods  mentioned 
above ;  but  more 
conveniently  by  Beil- 
stein's  plan,  in  which 
a  little  copper  oxide, 
supported  in  a  small 
loop  at  the  end  of  a 
platinum  wire,  is 
heated  in  a  Bunsen 
flame  until  this  is  no 
longer  coloured,"and 
is  then  used  to  con- 
vey a  small  portion 
of  the  substance 
adhering  to  the 

copper  oxide  into  the  flame.  If  chlorine  is  present  copper 
chloride  will  be  produced,  and  its  vapour  will  give  the  char- 
acteristic blue  and  green  flame  of  copper. 

Sulphur  and  Phosphorus  may  be  estimated  by  heating 
the  substance  with  fuming  nitric  acid  in  a  sealed  tube  (Carius's 
method  ;  see  under  Halogens).  The  sulphuric  acid  formed 
may  be  determined  as  barium  sulphate,  the  phosphoric  acid  as 
magnesium  pyrophosphate. 

In  the  case  of  the  less  volatile  substances,  a  dry  method 
may  conveniently  be  used,  in  which  fusion  in  a  silver  dish  with 
solid  potassium  hydrate,  and  gradual  addition  of  potassium 
nitrate,  is  employed  to  effect  the  oxidation  of  the  sulphur  to 
sulphuric  acid. 

Example.    .2178  gram  of  the  substance  gave  .2586  gram  of  BaSO4. 
The   percentage   of  sulphur    is   therefore,    since   233    parts   of   BaS'  >4 
contain  32  parts  of  S, 

.2^86      32 

— - — x  —  x  ioo 

.2178     233 

=  16.3. 


SULPHUR  AND  PHOSPHORUS 


The  qualitative  recognition  of  sulphur  or  phosphorus  in  an 
organic  body  may  be  effected  by  heating  the  dry  substance 
with  a  little  metallic  sodium.  If  sulphur  is  present,  sodium 
sulphide  will  be  formed,  and  may  be  detected  by  the  evolution 
of  H9S  on  addition  of  water  and  an  acid,  or  by  the  use  of 
sodium  nitro-prusside,  which  gives  an  intense  violet  colouration 
with  a  trace  of  soluble  sulphide.  In  the  case  of  phosphorus, 
sodium  phosphide  (or  if,  as  is  advantageous,  aluminium  filings 
be  employed,  aluminium  phosphide)  is  formed,  from  which 
the  dampness  of  the  breath  is  sufficient  to  evoke  the  character- 
istic smell  of  hydrogen  phosphide. 

Oxygen. — There  is  no  convenient  method  known  for  the 
detection  or  estimation  of  oxygen  in  a  compound.  Its  amount 
is  determined  by  difference,  i.e.,  by  subtracting  the  percentages 
of  all  the  other  elements  present  from  100,  and  taking  the 
remainder  to  represent  the  percentage  of  oxygen. 

QUESTIONS  ON  CHAPTER  'I 

1.  Describe  carefully  the  methods  you  would  use  for  the  quantitative 
estimation  of  the  elements  present  in  urea. 

2.  Explain  how  the  percentage  of  nitrogen  in  an  artificial  manure  can 
be  readily  determined. 

3.  Oil  of  mustard  contains  carbon,  hydrogen,  nitrogen,  and  sulphur. 
How  would  you  prove  that  these  elements  and  no  others  are  present  in  it  ? 

4.  How  is  the  percentage  of  chlorine  in  sodium  chloride  determined, 
and   how  must  the  method  be  modified  in  order  to  apply  it  to  organic 
substances  containing  chlorine  ? 


CHAPTER    II 
EMPIRICAL  AND   MOLECULAR  FORMUL/E 

THE  Empirical  Formula  of  a  substance  is  the  simplest 
formula  which  represents  the  results  of  analysis,  and  is 
calculated  from  these  in  the  following  way  :  Divide  the  per- 
centage of  each  clement  by  the  corresponding  atomic  weight  ; 
find  the  smallest  whole  numbers  standing  in  the  same  ratio  as 
the  quotients  thus  obtained,  and  you  will  have  the  indices  of 
the  formula.  This  is  best  illustrated  by  examples  : — 

A  substance  contains  the  percentages  given  below;   to  find  its  empirical 
formula 

C  =  40         per  cent. 

11=    6.66 

0  =  53-33       „ 

Then  €  =  ^=3.33 

6.66 
H  = ==6.66 

i 

0=^=3.33 

and  as  these  numbers  are  in  the  ratio  1:2:1,  the  empirical  formula  of  the 
substance  is  CHvO. 

In  the  above  example  wre  have  taken  not  the  results  of 
actual  analysis,  but  the  theoretical  percentages.  In  calculating 
from  the  experimental  numbers  —  always  more  or  less 
inaccurate — we  may  sometimes  have  to  choose  between  two 
or  more  formulae  which  agree  about  equally  well  with  the 
analytical  results.  In  such  cases  it  should  be  remembered 


MOLECULAR  FORMULAE  13 


that  we  usually  find  in  a  properly  conducted  analysis  :  (i.) 
about  .1  or  .2  per  cent  too  little  of  carbon,  unless  halogens 
are  present;  (ii.)  about  .2  per  cent  in  excess  of  hydrogen; 
and  (iii.)  about  .2  or  .3  per  cent  in  excess  of  nitrogen  (by 
Dumas's  method). 

The  chief  causes  of  these  slight  errors  are  :  (i. )  loss  of  CO2  through 
incomplete  absorption;  (ii. )  trace  of  moisture  in  the  copper  oxide 
employed  ;  (iii.)  presence  of  traces  of  air  in  the  combustion  tube  and  in 
the  CO2  used  for  expelling  air  from  the  tube. 

The  Molecular  Formula  represents  not  merely  the 
results  of  analysis,  but  is  also  in  agreement  with  whatever 
information  we  are  able  to  obtain  - —  by  application  of 
Avogadro's  hypothesis  or  otherwise — as  to  the  molecular 
weight  of  the  compound.  It  is  sometimes  identical  with  the 
empirical  formula,  but  is  often  a  multiple  of  it,  and  the  ratio 
is  ascertained  by  a  molecular  weight  determination.  This 
may  usually  be  effected  by  some  one  of  the  following  methods. 

I.  Chemical  Methods  are  not  of  very  general  application, 
and  give  only  a  minimum  value  of  the  molecular  weight. 
Their  principle  is  that  in  substituting  one  element  (or  radical) 
for  another,  we  cannot  replace  a  fraction  of  an  atom.  If,  then, 
in  a  particular  compound  it  is  found  possible  to  replace,  say, 
one  quarter  of  the  hydrogen  in  it  by  some  other  element, 
without  affecting  the  other  three  -  fourths,  we  conclude  that 
there  were  four  atoms  (or  a  multiple  of  four)  in  the  molecule 
of  that  compound. 

EXAMPLE  I.  The  analysis  of  acetic  acid  leads  to  the 
empirical  formula  CH0O  ;  but  there  are  numerous  derivatives 
of  the  acid  whose  analysis  shows  that  one-fourth  only  of  the 
hydrogen  has  been  replaced,  such  as  monochloracetic  acid 
C2H3C1O2,  silver  acetate  C9H.}AgO2,  etc.  Hence  the  molecu- 
lar formula  must  contain  four  atoms  of  hydrogen,  and  is 
written  C2H4O2. 

EXAMPLE  II.  Another  substance,  also  possessing  the  same 
empirical  formula  CH2O,  is  dextrose  ;  but  this  compound 
yields  a  derivative  in  which  analysis  shows  that  five-twelfths 
of  the  hydrogen  have  been  replaced,  while  seven-twelfths  are 
left ;  there  must  then  be  not  fewer  than  twelve  atoms  of 
hydrogen  in  the  molecule,  and  its  formula  is  put  as  C6H12O6. 


VAPOUR  DENSITY 


CHAP. 


II.  The  Physical  Methods  —  much  more  convenient, 
and  in  some  respects  more  decisive,  than  the  chemical — depend 
upon  the  "  law  of  Avogadro,"  or  upon  its  extension  by  Van't 
Hoff  to  the  case  of  dilute  solutions. 

As  applied  to  gases  the  law  states  that  at  a  given  tempera- 
ture the  pressure  of  a  gas  is  proportional  to  the  number  of 
molecules  in  unit  volume.  If  now  we  find  the  weights  of  equal 
volumes  (at  the  same  temperature  and  pressure)  of  two  gases, 
we  have  the  weights  of  equal  numbers  of  molecules  of  the 
gases,  and  the  ratio  of  these  weights  will  give  the  ratio  of  the 
molecular  weights.  The  vapour  density  of  a  substance  is 
the  ratio  obtained  by  comparing  the  weight  of  a  volume  of 
that  body  (in  the  gaseous  state)  with  the  same  volume  of 
hydrogen  at  the  same  temperature  and  pressure.  Admitting 
the  weight  of  the  hydrogen  mole- 
cule to  be  2,  in  accordance  with 
the  formula  H9,  it  follows  that, 
when  hydrogen  is  taken  as  the 
standard,  the  molecular  weight  of 
any  substance  is  twice  its  vapour 
de'isity.  In  determining  this  we 
do  not  need  to  measure  both 
vnpour  and  hydrogen  under  iden- 
tical conditions,  as  by  the  help 
of  Boyle's  and  Charles's  laws  we 
can  easily  reduce  the  results  ob- 
tained to  what  they  would  be 
under  the  same  pressure  and  tem- 
perature. The  experimental  pro- 
cesses which  may  be  used  for 
determining  vapour  densities  are 
many,  but  the  following  are  the 
most  important  : — 

(a.)  Victor  Meyer's  Method 
b>  V'  Meyer's  has  almost  entirely  supplanted  the 
older  ones  of  Hofmann  and  Dumas ; 
the  apparatus  employed  is  shown  in  Fig.  12.  A  cylindrical  bulb 
A,  provided  with  a  long  and  narrower  neck,  is  heated  to  a  steady 
temperature  by  some  suitable  means,  usually  by  the  vapour 
of  a  substance  kept  boiling  in  the  jacketing  tube.  When 


FIG.  12. — Apparatus  for  determining 


n  VICTOR  MEYER'S  METHOD  15 

the  temperature  has  become  quite  steady,  the  cork  is  removed, 
and  a  small  glass  tube  or  thin  bulb,  containing  about  half  a 
decigram  of  the  body  to  be  examined,  is  allowed  to  fall  into 
the  bulb,  the  cork  being  quickly  replaced.  In  order  that  the 
experiment  may  succeed,  it  is  necessary  that  the  temperature 
of  the  bulb  should  be  at  least  20°  or  30°  C.  above  the  boiling 
point  of  the  compound  under  investigation,  when  this  latter 
rapidly  evaporates,  and  in  doing  so  fills  the  lower  part  of  the 
bulb  with  vapour,  driving  out  through  the  side  tube  a 
corresponding  volume  of  air,  which  is  collected  in  E  and 
measured. 

It  calculating  the  result  it  is  unnecessary  to  know  the 
temperature  of  A  (it  must,  however,  be  steady).  The  vapour 
given  off  at  the  bottom  of  the  bulb  displaces  its  own  volume 
of  air,  but  this,  before  being  measured,  is  cooled  down  to  the 
temperature  of  the  water  over  which  it  is  collected.  What  we 
really  obtain  is,  therefore,  the  volume  which  the  vapour  of  the 
amount  of  substance  used  would  occupy  at  the  temperature 
and  pressure  in  E.  If,  then,  we  divide  the  weight  of  sub- 
stance used  by  the  weight  of  the  volume  V  of  hydrogen  (at 
the  temperature  and  pressure  in  E),  we  have  at  once  the 
vapour  density  of  the  compound  examined. 

The  results,  though  not  very  accurate,  are  practically  quite 
sufficient,  as  the  question  is  usually  not  one  of  determining 
the  exact  molecular  weight,  but  merely  of  the  ratio  of  the 
molecular  to  the  empirical  formula. 

Example.  .0623  gram  of  alcohol  gave  by  Victor  Meyer's  method 
31.5  c.c.  of  air,  measured  at  15°  C.  and  750  mm.  pressure. 

This  volume  would  become  31. 5  x  -~  x  ~-  c.c.  at  o°  C.  and  760  mm. ; 

200     700 

2Q.  ^ 

and  this  volume  of  hydrogen  (29.5  c.c.)  would  weigh  .0896  x  — '  —  gram. 
The  vapour  density  is  therefore 

.0623     1000  weight  of  substance 


.0896      29.5     weight  of  gas  obtained  reckoned  as  hydrogen 
or  23.6. 

(/?.)  Hofmann's  Method  is  still  occasionally  made  use  of 
for  substances  which  cannot  readily  be  vapourised  without  de- 
composition under  the  ordinary  pressure,  though  modifications 


16  HOFMANN'S  METHOD  CHAP. 

of  V.  Meyer's  method  have  also  been  made  for  this  purpose. 
A  long  graduated  tube,  closed  at  one  end,  is  filled  with  mercury, 
and  inverted  in  a  mercury  trough,  while  round  the  upper 
portion  of  the  tube  a  wider  jacketing  tube  is  placed,  through 
which  can  be  blown  the  vapour  of  some  liquid  of  suitable 
boiling  point.  A  small  glass  tube,  containing  about  a  fifth  of 
a  decigram  of  the  substance,  is  introduced  into  the  inner  tube, 
and  allowed  to  float  up  to  the  top  of  the  mercury,  where  its 
contents  are  then  vapourised  on  passing  a  current  of  steam  or 
other  vapour  through  the  outside  jacket. 

On  this  method  we  require  to  notice  the  volume  occupied 
by  the  vapour,  and  the  height  of  the  mercury  in  the  inner 
tube  above  its  level  in  the  trough,  besides  knowing  the 
temperature  of  the  jacketing  vapour.  Its  advantage  is  that  the 
substance  evaporates  under  a  pressure  considerably  less  than 
that  of  the  atmosphere,  in  consequence  of  its  partial  compensa- 
tion by  the  column  of  mercury  in  the  inner  tube. 

Example.  .0243  gram  of  substance  vapourised  at  the  temperature  of 
boiling  aniline  (183°  C.  )  gave  54.5  c.c.  ;  the  height  of  the  mercury 
column  was  420  mm.,  that  of  the  barometer  765  mm. 

Now  54.5  c.c.  of  hydrogen  at  345  mm.  pressure  (765  -  420)  and  183°  C. 
would  weigh 


54-5  xxx        =  .ooI33  gram 

hence  the  vapour  density  of  the  substance  is 


.00133 

Molecular  "Weight  of  Non-volatile    Substances.  — 

There  are  many  substances  of  which  it  is  quite  impossible  to 
determine  the  vapour  density,  as  they  are  not  volatile  without 
decomposition.  In  such  cases  we  can  obtain  assistance  by 
applying  methods,  first  established  experimentally  by  Raoult, 
depending  upon  certain  properties  of  solutions.  Van't  Hoff 
has  brought  forward  a  theory  by  which  these  various  facts  are 
connected  together,  but  for  the  purpose  in  view  the  experi- 
mental data  of  Raoult  are  sufficient. 

If  we  take  100  grams  of  water  or  any  other  solvent,  and 
dissolve  in  it  I  gram  of  any  substance,  it  is  found  that  (a)  the 
freezing  point  of  the  solution  is  lower,  and  (b]  the  boiling  point 


RAOULTS  METHOD 


is  higher  than  that  of  the  pure  solvent.  The  amount  of  change 
is  in  each  case  dependent  upon  the  molecular  weight  of  the 
dissolved  body.  For  the  same  solvent  the  change  is  proportional 
to  the  number  of  molecules  dissolved  in  a  given  quantity  of 
the  solvent. 

The  apparatus  devised  by  Beckmann  for  applying  the  first 
method,  depending  on  the  de- 
pression of  the  freezing  point,  is 
shown  in  Fig.  13.  About  20 
grams  of  the  solvent  are  intro- 
duced into  the  central  tube 
A  of  the  apparatus,  and  the  tem- 
perature being  slowly  brought 
down  below  the  melting  point, 
the  exact  temperature  at  which 
the  solvent  freezes  is  noticed 
on  the  thermometer.  A  small 
accurately  weighed  quantity 
of  the  substance  to  be  exam- 
ined is  now  introduced  into 
the  tube  A,  and  made  to 
dissolve  by  vigorous  stirring 
and  gentle  warmth ;  then  the 
temperature  is  again  lowered, 
and  when  freezing  occurs  the 
freezing  point  of  the  solution 
is  observed  on  the  thermo- 
meter. 


FIG.    13. — Beckmann 's    apparatus 
determining  molecular  weights. 


for 


Let  iv  =  weight  of  substance  used  ; 
W=          ,,  solvent  „ 

/  =  difference  between    freezing  point   of  the   solution 

and  freezing  point  of  solvent ; 
;;/  =  molecular  weight  of  the  substance  examined  ; 

then   the  number  of  molecules  of  the   substance  dissolved   in 

ftV 

W  grams  of  the  solvent  is  — ,  and  therefore  in   100  grams  of 
m 

the  solvent  there  would  be,  for  a  solution  of  the  same  strength, 

C 


1 8  RAO  LILTS  METHOD 


I  OO  IV 

,,7      molecules   dissolved.      According  to  Raoult's  results  the 

depression  of  the  freezing  point  for  the  solution  is  proportional 
to  this  number,  and  we  have 

i  oo  iv 


r^      7£/ 

or  ;*=iooA   — , 

where  A'  is  a  constant  depending  on  the  nature  of  the  solvent. 

The    values   of   K   for  the   most    important    solvents    are    as 

follows  : — 

Water  .          .  .          .          .19° 

Benzene  .....        49° 

Naphthalene  .....        74° 

Acetic  Acid  .....        39° 

For  further  particulars  of  this  method,  and  of  the  similar  one 
depending  on  the  elevation  of  the  boiling  point,  the  student 
may  advantageously  consult  Outlines  of  General  Chemistry, 
by  Ostwald,  p.  137,  or  Quantitative  Analysis,  by  Clowes  and 
Coleman,  p.  432. 

QUESTIONS  ON  CHAPTER  II 

1.  What   reasons   have  we   for  writing  the   formula  of  acetic  acid  as 
C2H4O-2  instead  of  the  simpler  one  CHL>O  ? 

2.  Describe   Victor    Meyer's   method  of   determining    vapour  density. 
Calculate  the  vapour  density   of  a  substance  from   the   following   data  : 
.0582  gram  of  the  substance  was  used,  and  23.5  c.c.  of  air  were  expelled 
(measured  at  18°  C.  and  755  mm.  pressure). 

3.  What  methods  can  be  used  to  determine  the  molecular  weight  of  a 
substance  such  as  sugar,  which  cannot  be  converted  into  vapour  without 
decomposition? 

4.  Butyric  acid  has  the  empirical  formula  CoH4O,  and  silver  butyrate 
is  found  to  contain  55.4  per  cent  of  silver  ;  what  do  you  conclude  from 
these  facts  as  to  the  molecular  formula  of  the  acid  ? 

5.  Calculate  the  molecular  weight  of  a  substance  from  the  following 
results  obtained  by  Raoult's  method  : — 

Weight  of  acetic  acid  taken  .  .  20.  5  grams 

Freezing  point  of  acetic  acid  .  .  16.435°  C. 

Weight  of  substance  dissolved  .  .  .1535  gram 

Freezing  point  of  solution  .  .  .  16.305°  C. 


CHAPTER    III 
HYDROCARBONS  OF  THE   METHANE   SERIES 

Methane  or  marsh  gas  is  theoretically  the  simplest  of  all 
the  compounds  of  carbon  and  hydrogen.  Analysis  shows  that  its 
empirical  formula  is  CH4,  and  the  fact  that  the  gas  is  eight  times 
heavier  than  hydrogen  indicates  the  molecular  weight  sixteen, 
and  shows  that  this  simplest  formula  is  also  the  molecular  one. 

It  occurs  naturally  in  the  gas  which  occasionally  comes  off 
in  bubbles  from  the  bottom  of  stagnant  ponds  ;  in  the  "  natural 
gas  "  escaping  from  fissures  in  the  earth  in  certain  oil-bearing 
districts,  and  constitutes  the  fire-damp  of  the  coal  miner  ; 
while  ordinary  coal-gas  contains  about  one-third  of  its  volume 
of  methane. 

Of  methods  used  in  the  laboratory  the  three  following  are 
important,  the  first  from  the  theoretical  standpoint,  and  the 
two  latter  from  that  of  practical  work  :  — 

1.  Methane  can  be  synthesised,  i.e.  built  up  from  inorganic 
materials,   by  passing  a  mixture  of  H2S  with  vapour  of  CS2 
over  red-hot  copper  : 

2H2S  +  CS2  +  8Cu  -  CH4  +  Cu,S. 

2.  A  convenient  laboratory  method,   yielding,    however,   a 
somewhat  impure  methane,  is  to  heat  cautiously  a  mixture  of 
sodium  acetate  with  sodium  hydrate  (barium  hydrate   gives  a 
less  impure  gas)  : 


N,iC2H302    +    NaOH  =  Na2C03    +    CH4 
Sodium  acetate.  Methane. 


METHANE 


CHAP. 


If  a  glass  vessel  be  used,  it  will  soon  be  attacked  by  the  melted 
caustic  soda  ;  and  though  this  action  can  be  lessened  by  using 
an  admixture  of  quicklime  (soda-lime  is  best),  it  is  more  con- 
venient when  possible  to  employ  a  copper  retort. 


FIG.  14.  —  Apparatus  for  the  preparation  of  CH4  from  sodium  acetate  and 
soda-lime. 


EXPT.  3.  Prepare  marsh  gas  by  heating  some  dry  anhydrous  (not 
crystallised)  sodium  acetate  with  about  four  parts  of  powdered  soda-lime 
in  a  small  glass  flask  fitted  with  cork  and  delivery  tube.  Collect  two  jars 
of  the  gas  and  examine  its  behaviour,  (a)  when  a  lighted  taper  is  brought 
near,  (^)  when  allowed  to  mix  with  bromine  vapour  contained  in  a  second 
jar. 

3.  Pure  methane  is  best  prepared  by  the  action  on  methyl 
iodide,  CH.^1,  of  the  zinc-copper  couple  in  presence  of  alcohol. 
The  couple  is  merely  zinc  covered  with  a  deposit  of  copper  by 
treatment  with  a  solution  of  copper  sulphate,  and  acts  in  pres- 
ence of  cither  water  or  alcohol  as  an  excellent  reducing  agent  : 


CH. 


+    H0     =     CH 


4     + 
Methane. 


HI. 


Methyl  iodide. 
A  more  complete  representation  is  given  by  the  equation  : 


CH3I  +  Zn  +  C2H60  =  Zn  5  +  CH4. 


Methane  is   a  colourless  gas,  without  taste  or  smell,  only 


in  HOMOLOGY 


slightly  soluble  in  water,  and  very  difficult  to  condense  to  a 
liquid.  It  burns  in  the  air  with  a  nearly  non-luminous  flame, 
which  becomes  much  brighter  if  both  the  air  and  the  methane 
are  strongly  heated  before  combustion  (regenerative  burners), 
and  the  products  of  the  burning  are  water  and  carbon  dioxide  : 

CH4  +  2O2  =  CO2  +  2  H2O. 

A  mixture  of  i  vol.  CH4  with  2  vols.  O2  explodes  violently 
when  ignited.  When  strongly  heated  alone,  methane  is 
decomposed  with  formation  of  carbon,  hydrogen,  and  smaller 
quantities  of  other  products. 

Methane  is  a  very  stable  substance,  and  is  not  readily 
attacked  even  by  the  most  active  reagents.  Nitric  acid  is 
almost  without  action  upon  it ;  chlorine  and  bromine  attack  it 
slowly  (more  quickly  in  sunlight  than  in  the  dark)  with  forma- 
tion of  "  substitution  products,"  in  which  one  or  more  hydrogen 
atoms  of  the  methane  have  been  expelled  (in  combination  with 
Cl  or  Br  as  HC1  or  HBr)  and  their  place  taken  by  halogen 
atoms  : 

CH4  +  Br2  =  CH3Br  +   HBr, 
Methyl  bromide. 

or  CH4  +  2Br2    =    CH2Br2    +    2 HBr,  etc. 

Methylene  bromide. 

Homology. — Methane  is  the  lowest  member  of  a  series  of 
hydrocarbons,  all  of  which  can  (in  general)  be  prepared  by 
similar  reactions,  and  strongly  resemble  one  another  in  their 
chemical  behaviour.  Each  member  differs  from  the  one  below 
it  in  the  series  by  the  replacement  in  its  formula  of  an  H  atom 
by  the  group  CH3,  to  which  the  name  methyl  is  given  ;  the  nett 
difference  between  any  two  successive  members  is  therefore 
CH2.  Such  a  series  is  called  a  homologous  series,  and  the 
study  of  organic  chemistry  is  much  simplified  by  the  possi- 
bility of  classifying  in  this  way  the  immense  number  of  known 
compounds  into  groups  of  similar  bodies. 

Starting  from  methane,  CH4,  we  have  as  the  formula  of 
the  next  member  of  the  series  CH4  +  CH9  or  C2H6,  for  the 
third  CaH8,  and  so  on  up  to  C60H102,  the  highest  which  has 
yet  been  prepared.  The  generic  formula  is  C,,HOM+0. 


ETHANE 


CHAP. 


Ethane,  C2H6,  stands  next  to  methane,  and  can  be  prepared 
by  similar  reactions.  In  the  first,  we  start  not  from  sodium 
acetate  (as  for  methane),  but  from  the  sodium  salt  of  the  acid 
next  above  acetic  in  the  very  important  series  of  homologous 
acids,  of  which  acetic  forms  the  second  and  propionic  the  third 
member.  Acetic  acid  is  C2H4O2  and  propionic  C3HGO<,.  We 
proceed  then  as  follows  : — 

i.   Sodium  propionate  is  heated  with  sodium  hydrate, 

NaC.,HrO9     +     NaOH  =  Na0COQ    +    C0H,, 

o      5     2  23  26 

Sodium  propionate.  Ethane. 

when  ethane  is  evolved  and  sodium  carbonate  remains. 


FIG.  15. — Apparatus  for  preparing  C^H^  from  ethyl  iodide  by  the  action  of  the 
zinc-copper  couple. 

2.  In  the  second  method  for  preparing  ethane,  ethyl  iodide, 
C.,Hr(I  (homologous  with  methyl  iodide,  CH^I),  is  reduced  with 
the  zinc-copper  couple  : 


HI  PROPANE  AND  BUTANE  23 

C3H5I    4-   H2    =    C2H6    +    HI. 
Ethyl  iodide.  Ethane. 

3.  A  third  method  is  of  a  type  applicable  only  to  the  pre- 
paration of  those  members  of  the  series  which  contain  an  even 
number  of  carbon  atoms  in  the  molecule.  In  this  case  we 
start  from  methyl  iodide,  CH3I,  and  by  treating  it  with  metallic 
sodium,  abstract  the  iodine  and  cause  two  methyl  residues — 
CH., — to  unite  : 

o 

2CH3I    +   2Na  =  2NaI  +  C2H6. 
Methyl  iodide.  Ethane. 

In  accordance  with  this  method  of  preparation,  the  formula  of 
ethane  may  be  written  CH3  .  CH;r 

Ethane  is  a  combustible  gas,  and  burns  with  a  more  lumin- 
ous flame  than  methane.  It  resembles  that  gas  very  greatly 
in  chemical  behaviour,  and  reacts  in  the  same  way  with  the 
halogens,  forming  substitution  products,  such  as 

C2H0  +  C12    =    C2H5C1    +    HC1. 
Ethane.  Ethyl  chloride. 

Propane,  C3H8  (  =  C2H6  -f-  CH2),  stands  next  above  ethane. 
It  may  be  prepared  by  methods  corresponding  to  the  first  two 
of  those  given  for  ethane.  The  best  is  the  following  : 

i.  Propyl  iodide,  C3H7I  (  =  C2H&I  +  CH2),  is  reduced  with 
the  zinc-copper  couple  : 

C,H7I     +     H9  =  C.,HR    +    HI. 

pi  21  9       0 

Propyl  iodide.  Propane. 

Butane  is  the  name  given  to  the  next  hydrocarbon  of  this 
series  with  the  formula  C4H1Q.  We  here  encounter  for  the  first 
time  a  fact  of  very  great  importance  :  that  there  may  be,  and 
often  are,  more  substances  than  one  corresponding  to  a  parti- 
cular molecular  formula.  This  experimental  fact  we  interpret  to 
mean  that  two  molecules,  each  containing  the  same  atoms  in 
the  same  number,  may  yet  be  distinct  both  chemically  and 
physically  ;  and  this  difference  we  explain  as  being  clue  to  the 
different  arrangement  of  the  atoms  in  the  molecule.  The 
name  isomerism  is  given  to  this  phenomenon,  and  substances 


24  ISOMERISM  CHAP. 

which  possess  identical  molecular  composition,  and  yet  differ 
from  one  another  in  the  way  described,  are  said  to  be  isomeric. 
In  the  majority  of  such  cases  it  is  found  possible  to  give  a 
reasonable  representation  of  the  different  chemical  behaviour 
of  the  isomeric  bodies  by  structural  formula,  which  are  also 
considered  to  represent  more  or  less  exactly  the  actual  grouping 
of  the  atoms  inside  the  molecule.  Let  us  now  consider  more 
fully  this  particular  case  of  the  butanes. 

In  the  first  three  members  of  this  series  no  isomerism  has 
been  found  to  exist.  Their  formulae,  CH4,  C2Hg,  C3H8,  may  be 
expanded  into  CH4,  CH3.CH3,  CH3.CH2.CH3,  which  are  in 
agreement  with  the  valency  hypothesis,  and  represent,  more 
completely  than  the  simple  formulae  do,  the  modes  of  formation 
and  general  chemical  behaviour  of  the  three  substances.  In 
each  case  the  formula  is  obtained  from  that  of  the  next  lower 
compound  by  substituting  methyl,  CH3,  for  hydrogen.  In 
methane  there  are  four  hydrogen  atoms  in  the  molecule,  but 
these  are  all  similarly  circumstanced,  and  whichever  of  them 
be  replaced  we  obtain  the  same  ethane,  CH3  .  CH;r  Similarly, 
when  we  proceed  from  this  to  propane  ;  the  six  hydrogen  atoms 
in  the  ethane  molecule  are  all  of  equal  value,  and  we  get 
always  the  same  propane  when  any  one  of  them  is  substituted  by 
a  methyl  group.  But  at  the  next  step  this  is  no  longer  the  case, 
for  the  eight  hydrogen  atoms  in  propane  are  not  all  similarly 
placed  ;  while  six  of  them  are  alike,  and  the  other  two  also 
like  one  another  in  position,  there  is  a  difference  between  the 
atoms  attached  to  the  two  terminal  carbon  atoms  and  those 
which  are  connected  to  the  carbon  atom  in  the  centre  of  the 
chain.  Hence  two  formulae  for  butane  may  be  deduced  from 
that  of  propane  by  substituting  CH3  for  H  atoms  of  different 
value  : 

CH3  .  CH2  .  CH3  gives  (i)  CH0 .  CH., .  CH2  .  CH., 
and     (2)  CH3.  CH".  (CH3)2. 

So  far  by  paper  work.  Experimental  investigation  has  proved 
that  there  are  two  butanes,  each  with  the  formula  C4HJO,  and 
each  rightly  placed,  according  to  its  general  behaviour,  in  the 
methane  series. 

Of  these  two  butanes  one  is  prepared  from  ethyl  iodide  by 
abstracting  the  iodine  with  sodium  : 


PENTANE 


2CH3.  CH2 

Ethyl  iodide. 


.  OH.,.  CH,,.  CHo, 
Normal  butane. 


and  this  mode  of  formation  is  well  represented  by  the  formula 
given  in  the  above  equation.  This  particular  butane  is  called 
normal  butane,  or  simply  butane.  For  the  other  butane  the 
formula  CH3 .  CH  .  (CH3)0  remains,  and  the  name  given  to  it  is 
isobutane. 

Pentane,  C&H10,  is  the  generic  name  of  the  isomeric  hydro- 
carbons corresponding  to  the  formula  given.  If  we  attempt  to 
work  out  the  number  of  isomers  which  may  in  accordance  with 
the  valency  theory  be  obtained,  we  find  that  three  are  possible  ; 
and  experimental  work  has  enabled  us  actually  to  prepare 
isomeric  pentanes,  and  to  assign  to  each,  one  of  the  three 
formulae  indicated  by  theory. 

The  most  important  is  normal pentane,  CH3.CH0.CH2.CH2. 
CH3,  which  is  contained  in  crude  petroleum,  and  can  be  isolated 
from  it  as  a  volatile  inflammable  liquid  boiling  at  37°.  This 
has  been  used  as  a  means  of  obtaining  a  reliable  standard  of 
illumination  for  photometric  purposes. 

The  following  table  illustrates  the  isomerism  of  the  butanes 
and  pentanes  : — 


NAME. 

FORMULA. 

PREPARATION. 

Normal  Butane 

CH3.CH2.CH;,.CH3 

From  ethyl  iodide  and  zinc  dust  : 

2CH3  .  CH2I  +  Zn  =  C4H10  +  ZnI2 

Isobutane 

CH3.CH2:(CH3), 

From  isobutyl  iodide  by  reduction  : 

Normal  Pentane 

CH3.CHo.CH2.CH2.CH3 

Separated  from  petroleum. 

Isopentane 

CH3.CH2.CH  :(CH3)2 

(Dimethyl-ethyl- 

methane) 

Tetra-methyl- 

C(CH3)4 

methane 

Petroleum  and  Paraffin. — In  various  parts  of  the  world, 
more  especially  in  Pennsylvania  and  in  Baku,  a  province  of 
Southern  Russia,  oil-bearing  strata  occur  from  which  an  in- 


26  PETROLEUM  CHAP. 

flammable  oil  can  be  obtained.  Wells  are  drilled  through 
the  overlying  layers  of  earth  until  the  oil  is  struck  at  a  depth 
varying  from  50  to  2000  feet  and  over.  In  many  cases  the 
newly-opened  well  "  spouts  "  oil,  frequently  with  uncontrollable 
violence,  but  as  the  original  gas-pressure  declines,  it  becomes 
necessary  to  have  recourse  to  pumping.  The  crude  oil  requires 
to  be  refined,  and  both  in  America  and  in  Russia  this  process  is 
carried  on,  not  at  the  wells  themselves,  but  at  large  refineries 
conveniently  situated  for  export.  The  oil  is  transported  to  the 
refineries  by  means  of  long  lines  of  pipes,  through  which  it  is 
forced  by  powerful  pumps. 

Investigation  has  shown  that  American  and  Russian  petro- 
leums differ  essentially  in  chemical  composition.  American 
petroleum  is  almost  entirely  a  mixture  of  various  hydrocarbons 
of  the  methane  series  from  CH4  itself  up  to  solid  hydrocarbons 
of  very  high  molecular  weight.  The  refining  of  the  crude  oil 
has  for  its  chief  purpose  the  separation  of  this  complex  mixture 
into  a  number  of  fractions,  and  is  accomplished  by  distillation. 
The  more  volatile  portions  are  the  first  to  come  over,  and  are 
followed  by  others  of  higher  and  higher  boiling  points.  The 
most  important  fractions  are  : — 

(1)  Gasoline,   B.P.   3o°-ioo°,   used    for  making   "oil-gas," 
which  is  simply  air  saturated  with  vapour  of  gasoline. 

(2)  Petroleum  proper,  B.P.  I  5o°-3oo°,  used  in  lamps. 

(3)  Higher  boiling  portions  from  which  lubricating  oils  and 
vaseline  are  obtained. 

Russian  petroleum  contains  only  a  very  small  percentage  of 
hydrocarbons  of  the  methane  series,  the  chief  bulk  being 
"  naphthenes  "  of  the  generic  formula  Cnli2u.  These  are  dis- 
tinct from  the  olefines  of  the  same  formula,  and  will  not  be 
considered  until  the  second  part  of  this  book  in  connection 
with  the  benzene  hydrocarbons,  from  which  they  are  derived. 
The  products  obtained  by  refining  the  Russian  crude  oil  are 
very  similar  to  those  from  American  petroleum,  but  a  larger 
yield  of  oils  suitable  for  lubricating  machinery  is  got,  and  the 
residue  is  not  usually  worked  up  for  a  vaseline-like  product,  but 
is  generally  employed  as  fuel. 

Another  important  source  of  hydrocarbons  of  the  methane 


PARAFFIN  27 


series  is  the  destructive  distillation  of  bituminous  shale  or 
other  material  of  similar  composition.  This  process  is  largely 
carried  on  in  the  south-west  of  Scotland,  and  from  the  products 
various  valuable  mixtures  of  hydrocarbons  are  separated  by 
refining.  One  of  these  is  "  paraffin  oil "  ;  another  is  the  white 
solid  "paraffin  wax,"  and  both  are  made  up  almost  exclusively 
of  hydrocarbons  of  the  methane  series. 

Properties  of  the  Hydrocarbons,  CflH2n+iy. — All  the 
hydrocarbons  of  this  homologous  series,  from  marsh  gas  itself  up 
to  the  highest  member  yet  obtained,  present  an  almost  complete 
resemblance  in  chemical  behaviour.  They  are  all  very  inert 
substances,  not  attacked  by  nitric  acid,  and  only  gradually 
acted  upon  by  chlorine  or  bromine.  The  products  formed  by 
the  action  of  the  halogens  are  substitution  products,  in  which 
some  of  the  hydrogen  of  the  hydrocarbons  has  been  replaced 
by  chlorine  or  bromine.  In  no  case  are  addition  products 
formed  by  the  members  of  this  series. 

The  physical  properties  of  the  members  change  gradually 
as  we  pass  from  one  end  of  the  series  to  the  other.  The  lowest 
members  are  gases  requiring  great  pressure  or  cold  to  convert 
them  into  liquids  ;  the  pentanes  are  volatile  liquids,  and, 
ascending  the  series,  we  come  to  liquids  of  higher  and  higher 
boiling  point  ;  while  still  farther  up  the  series  we  meet  with 
hydrocarbons  which  are  solid  at  the  ordinary  temperature. 


QUESTIONS  ON  CHAPTER  III 

1.  Describe  the  preparation  and  properties  of  methane. 

2.  Methane  and  ethane  are  members  of  a  homologous  series  ;  show 
the  bearing  of  this  statement   upon   the  properties   of  the  gas  and   the 
methods  used  for  their  preparation. 

3.  What  is  meant  by   isomerism  ?     Deduce   the  formula   of  the  two 
isomeric  butanes  from  that  of  propane. 

4.  What  substances  are  contained  in  crude  petroleum  ?     What  com- 
mercial products  are  obtained  from  it,  and  by  what  processes  ? 


CHAPTER    IV 
OLEFINES    AND    ACETYLENE 

THE  defines  form  a  second  series  of  hydrocarbons,  of  which 
the  starting-point  is  ethylene,  C2H4.  The  succeeding  homologues 
differ  always  by  CH2,  and  it  thus  follows  that  every  member 
of  the  series  has  the  same  percentage  composition.  They  differ, 
of  course,  in  molecular  weight,  and  therefore  in  vapour  density. 
The  generic  formula  is  CnH.2n,  and  while  we  again  find  the 
same  similarity  in  general  chemical  behaviour  between  all  the 
defines,  as  between  all  the  hydrocarbons  of  the  CwH2M+2 
series,  there  are  important  differences  between  the  two  separate 
series.  The  chief  of  these  are  summed  up  in  the  contrast  of 
the  two  terms  saturated  and  unsatiirated,  applied  respectively 
to  the  methane  and  to  the  olefine  series. 

Ethylene,  C2H4,  is  the  lowest  known  member  of  the  series, 
and  as  in  every  reaction  where  we  should  expect  a  substance, 
CH2,  to  be  produced  we  obtain  instead  C2H4,  it  seems  estab- 
lished that  no  compound  of  the  formula  CH2  can  exist.  The 
most  convenient  way  of  preparing  ethylene  is  by  the  action  of 
concentrated  sulphuric  acid  upon  ethyl  alcohol,  C2H6O,  a 
reaction  which  may  very  concisely  be  represented  thus  : 

C2H6O     -     H2O    ==    C2H4. 
Ethyl  alcohol.  Ethylene. 

What  really  happens  is  that  ethyl-sulphuric  acid,  C2H.  .  HSO4, 
is  first  produced,  and  this,  when  heated,  decomposes  into 
ethylene  and  sulphuric  acid  : 


ETHYLENE 


29 


C2H5OH     + 

Ethyl  alcohol. 


H2S04    = 


C2H5 


HS0 


H20 


Ethyl-sulphuric  acid. 


C2H5 

EXPT.  4.  Prepare  ethylene  by  heating  in  a  capacious  flask  (2  litres)  a 
mixture  of  40  c.c.  methylated  spirit  with  200  c.c.  concentrated  H2SO4 
along  with  some  sand,  to  prevent  frothing.  The  gas  can  be  purified 
from  SO-j  and  other  impurities  by  washing  with  solution  of  caustic  soda, 
and  can  be  collected  over  water. 


FIG.  16.  —  Preparation  of  Ethylene  from  alcohol  and  sulphuric  acid. 

Ethylene  is  a  colourless  gas  with  a  faint  sweetish  smell,  and 
burns  in  the  air  with  a  bright  yellow  flame.  Like  all  the 
other  members  of  the  series,  it  is  an  unsaturated  compound, 
being  able  to  unite  directly  with  several  substances  —  Cl,  Br,  I, 
H,  HI,  etc.,  —  nothing  being  driven  out  from  the  ethylene 
molecule  to  be  replaced  by  the  substituting  atoms.  This  is 
explained  on  the  valency  hypothesis  as  due  to  those  carbon 
valencies  which  are  unsaturated  in  the  molecule  of  ethylene. 

Ethylene  combines  readily  with  Cl,  Br,  and  I  (in  alcoholic 
solution)  at  the  ordinary  temperature,  with  hydrogen  when  the 
two  mixed  gases  are  passed  over  platinum  black  ;  ethane  or 
a  derivative  of  it  is  in  each  case  the  product.  When  passed 
into  concentrated  H2SO4,  ethylene  is  absorbed  and  ethyl- 
sulphuric  acid  is  formed  : 


C2H4 


H2SO4  =  C2H5  .  HSO4. 


3o  PROPYLENE  CHAP. 

EXPT.  5.  Fill  two  jars  with  ethylene  and  bromine  vapour  ;  bring 
them  together  mouth  to  mouth.  The  colour  of  the  bromine  is  rapidly  dis- 
charged, and  small  oily  drops  of  a  liquid  —  ethylene  dibromide  —  are  formed: 


Try  a  similar  experiment  with  methane  and  bromine.  In  this  case  the 
action  takes  place  slowly,  and  the  bromine  makes  its  way  into  the  methane 
molecule  only  by  expelling  some  of  the  hydrogen  : 

CH4+  Br2  =  CH3Br+  HBr. 
Methane  is  termed  a  saturated  compound,  whereas  ethylene  is  unsaturated. 

Propylene,  C3H6,  is  obtained  most  conveniently  by  a 
reaction  typical  of  a  second  general  method  of  preparing  the 
defines.  Isopropyl  iodide,  C3H7I,  a  halogen  derivative  of  the 
corresponding  hydrocarbon  of  the  methane  series  (in  this  case 
C3Hg),  is  treated  with  an  alcoholic  solution  of  potash,  whereby 
one  atom  of  hydrogen  and  one  of  the  halogen  are  abstracted  : 

C3HVI      +      KOH    =    C3H6    +    KI  +  H,0. 

Isopropyl  iodide.  Propylene. 

The  formula  of  the  isopropyl  iodide  is  CH3.  CHI  .  CH3.  The 
C3H6  obtained  from  this  by  abstraction  of  HI  may  be  either 
CH3.  C  .  CH3  or  CH3  .  CH  :  CH2,  but  the  first  formula  is  nega- 
tived by  numerous  facts,  of  which  a  very  conclusive  one  is  that 
propylene  furnishes  three  isomeric  chloro-propylenes,  C3H5C1. 
This  is  readily  explained  by  the  second,  but  is  quite  inconsist- 
ent with  the  first.  The  two  dots  in  the  correct  formula  indicate 
that  the  two  carbons,  one  on  either  side,  are  each  capable  of 
further  uniting  with  an  additional  atom,  and  are  connected 
together  in  a  different  manner  from  that  prevailing  between 
carbon  atoms  which  are  exerting  their  maximum  valency.  Two 
such  carbon  atoms  as  those  we  have  been  considering  in  the 
propylene  molecule  are  said  to  be  united  by  an  ethylene 
linkage,  or  by  a  double  bond;  but  it  must  not  be  imagined 
from  the  latter  expression  that  such  atoms  are  more  firmly 
held  together  than  those  united  in  the  ordinary  way  (single 
bond).  As  a  matter  of  fact,  an  unsaturated  molecule  when  it 
suffers  decomposition  usually  breaks  up  most  readily  at  the 
so-called  double  bond.  Thermo-chemical  investigation  also 
shows  that  an  ethylene  linkage  cannot  be  regarded  as  simply 


IV  VAN'T  HOFF'S  TETRAHEDRAL  THEORY  31 

the  double  of  single  linkage  ;  there  is  a  real  difference  in  kind 
between  those  two  modes  in  which  carbon  atoms  may  be 
connected. 

Great  assistance  in  correlating  a  very  large  number  of  ex- 
perimental facts  is  furnished  by  the  tetrahedral  theory  of  the 
carbon  atom,  which  was  proposed  by  Van't  Hoff  in  1877,  and 
has  since  been  extended  by  Wislicenus  and  other  chemists. 
According  to  this  valuable  hypothesis,  the  carbon  atom  is  re- 
garded as  being  similar  in  shape  to  a  regular  tetrahedron,  a 
solid  figure  bounded  by  four  equilateral  triangles,  and  two 
carbon  atoms  may  be  connected  together  in  the  following 
three  ways  : 

a.  Simple  linkage  :  the  two  tetrahedra  are  in  contact  at  a 
corner  of  each. 

b.  Double  linkage  :  the  two  tetrahedra  are  in  contact  along 
an  edge  of  each. 

c.  Triple  linkage  :  the  two  tetrahedra  have  a  whole  face  of 
each  in  contact. 

The  first  kind  of  linkage  is  exemplified  in  the  case  of  ethane, 
the  second  in  ethylene,  and  the  third  in  acetylene.  Substances 
which  contain  a  double  or  triple  linkage  are  unsaturated,  and 
the  theory  affords  a  clear  representation  of  the  way  in  which 
an  unsaturated  body  becomes  saturated  by  addition  of  chlorine, 
bromine,  etc.  The  following  diagrams  will  illustrate  these 
points  better  than  any  verbal  explanations. 

To  return  to  propylene  :  the  theory  which  we  have  been 
considering  embodies  very  conveniently  a  large  number  of  ex- 
perimental generalisations,  among  them  this,  that  such  a 
formula  as  CH3.C.CH3,  in  which  carbon  acts  as  a  divalent 
element,  represents  an  arrangement  of  atoms  incapable  of 
permanent  existence.  We  have  already  seen  reason  to  reject  it 
in  favour  of  the  alternative  CH3.  CH  :  CH2. 

There  are  a  few  exceptional  cases  in  which  carbon  is  divalent,  and 
where  it  is  therefore  necessary  to  suppose  that  two  of  the  four  corners  of 
the  carbon  tetrahedron  are  unemployed,  e.g.  CO. 

Butylene,  C4H8,  the  next  member  of  the  series,  furnishes 
an  instance  of  isomerism.  There  are  three  isomeric  butylenes, 
all  of  which  may  be  looked  upon  as  derived  from  ethylene  by 


BUTYLENE 


CHAP, 


replacement  of  hydrogen  by  methyl  or  ethyl  groups,  and  their 
names  are  best  chosen  to  represent  the  manner  of  this 
derivation  : 

a.  Symmetrical  dimethyl-ethylene,  CH0 .  CH  :  CH  .  CH3. 

b.  Unsymmetrical  dimethyl-ethylene,  CH., :  C(CH3)2. 

c.  Ethyl-ethylene,  C,H5CH:CH2. 


FIG.  17. — Representation  of  carbon  atoms  linked  together  as  in 
(A)  Ethane,  (B)  Ethylene,  (C)  Acetylene. 


The  names  are  somewhat  cumbrous,  but  have  the  advantage 
of  telling  as  much  about  the  substances  as  the  formulas  them- 
selves ;  they  are,  in  fact,  merely  the  formulae  in  words  instead 
of  symbols.  The  methods  by  which  these  three  isomers  have 
been  prepared  are  too  complicated  for  us  to  enter  into  ;  the 


ACETYLENE 


33 


important  thing  is  that  the  theoretical  number  of  isomers  have 

been  obtained. 

Acetylene,  C2H9,  is  the  lowest  member  of  another  series 

of  unsaturated  hydrocarbons.      In  this  we  have  a  triple  linkage 

between  the  carbons,  so  that  only  two  hydrogen  atoms  can  be 

attached  to  them,  one  to  each  :   HC  ;  CH. 

Acetylene  can  be  made  by  several  different  reactions  : — 
(i)   By    heating     ethylene     dibromide,    C2H4Br2,    with    an 

alcoholic  solution  of  potash  : 


FIG.  18.  —  Preparation  of  Acetylene  by  the  action  of  alcoholic  potash  on  ethylene 
bromide  ;  both  flasks  contain  potash,  and  the  bromide  is  allowed  to  drop 
slowly  from  the  tap-funnel  into  the  heated  potash  in  the  first  flask. 

CH0Br  .  CHQBr  -  2HBr=  HC  !  CH. 
Ethylene  bromide.  Acetylene. 

(2)  By  direct  combination  of  carbon  and  hydrogen,  when 
the  electric  arc  is   passed  between  carbon  poles   in  an  atmo- 
sphere of  hydrogen. 

(3)  By  the  action  of  water  upon  barium  carbide  : 


BaC2     + 
Barium  carbide. 


2H.OH   =  C,H2 

Acetylene. 
D 


Ba(OH)2. 


34 


ACETYLENE 


This  is  a  very  convenient  method  of  preparing  the  gas 
when  it  is  wanted  in  considerable  quantity. 

(4)  By  the  degraded  combustion  of  coal-gas,  such  as 
occurs  when  the  temperature  of  the  flame  is  artificially 
lowered  by  contact  with  a  metal  surface  (a  Bunsen  burner  in 
which  the  gas  is  burning  at  the  bottom  of  the  brass  tube)  : 


Ethane. 


02  =  C2H2  +  2H20. 

Acetylene. 


Acetylene  is  a  colourless  gas  with  an  unpleasant  smell. 
It  is  soluble  in  about  its  own  volume  of  water,  and  burns  in 
the  air  with  a  bright  smoky  flame.  The  most  remarkable 
chemical  characteristic  of  acetylene  is  its  property  of  forming 
explosive  compounds  containing  copper  or  silver.  By  means 
of  these  compounds  acetylene  can  be  readily  detected  and 
isolated  from  its  mixture  with  other  gases. 


FIG.  19.  —Preparation  of  Acetylene  by  the  degraded  combustion  of  coal-gas. 

EXPT.  6.  Prepare  some  cuprous  chloride,  CuCl,  by  passing  SO2  gas 
into  a  solution  of  90  grams  NaCl  and  200  grams  crystallised  CuSO4  until 
the  gas  is  no  longer  absorbed  ;  pour  into  about  half  a  litre  of  water,  and 
filter.  The  white  precipitate  of  CuCl  is  collected,  and  dissolved  in  some 
strong  ammonia  solution. 

Open  wide  the  air-holes  of  a  large  Bunsen  burner,  and  light  the  gas  at 
the  bottom  of  the  tube.  Over  the  burner  support  a  funnel,  which  is  con- 
nected with  a  gas-washing  bottle  containing  the  ammoniacal  solution  of 
cuprous  chloride.  Join  the  other  tube  of  the  wash-bottle  to  an  aspirator, 
and  draw  a  steady  current  of  air  through  the  apparatus. 


IV 


ACETYLENE 


35 


A  dark  red  precipitate  will  form  in  the  solution  of  cuprous  chloride. 
This  has  the  composition  C-jHCu,  and  when  dry  explodes  on  being 
heated,  or  if  struck  between  two  metal  surfaces.  Acetylene  can  be 
recovered  from  it  by  treatment  with  dilute  hydrochloric  acid. 


Acetylene  unites  readily  with  hydrogen,  when  the  two  gases 
are  passed  over  platinum  black,  to  form  ethane  : 


CH 

Acetylene. 


FIG.  20.— Representation  on  the  tetrahedral  theory  of  the  conversion  of  Acetylene 
into  dichlor-ethylene  and  tetrachlor-ethane  by  the  action  of  chlorine. 


Chlorine  is  without  action  upon  the  pure  gas  in  the  dark, 
but  in  sunlight  dichlor-ethylene  and  tetrachlor-ethane  are 
successively  formed  : 


36  ACETYLENE  CHAP,  iv 


(a)  CH!CH  +  C12  =  CHC1:CHC1, 

Acetylene.  Dichlor-ethylene. 

(b)  CHC1  :  CHC1  +  Cl.,  =  CHQ2  .  CHC1.2. 

Dichlor-ethylene.  Tetrachlor-ethane. 

These  changes  are  represented  on  the  tetrahedral  theory  by 
the  diagrams  in  Fig.  20. 


QUESTIONS  ON  CHAPTER  IV 

1.  What  is  the  chief  difference  in  chemical  behaviour  between  a  satur- 
ated and  an  unsaturated  compound  ? 

2.  Give  the  preparation  of  acetylene  and  the  most  important  properties 
of  the  gas. 

3.  Give    an    elementary   account    of   the   tetrahedral  theory  of   Van't 
Hoff  as    applied    to    explain    the    structure    of    the    three    hydrocarbons 
C2H6,   C2H4,   C2H2. 

4.  How   is   ethylene   made  ?     What  is  formed  when  it  is  passed  into 
concentrated  sulphuric  acid  ? 

5.  How   could    you    prepare   ethane   from    the   elements    carbon   and 
hydrogen  ? 


CHAPTER    V 
HALOID   DERIVATIVES 

IN  any  hydrocarbon  it  is  generally  possible  to  replace  from 
one  up  to  the  full  number  of  hydrogen  atoms  present  in  the 
molecule,  by  chlorine,  bromine,  or  iodine. 

Methyl  Chloride,  CH3C1,  is  the  first  to  be  considered  of 
all  these  haloid  derivatives  ;  it  may  be  prepared 

1.  By  the  direct  action  of  chlorine  upon  methane,  according 
to  the  equation  : 

CH4  +  C12  =  CH8C1  +  HC1, 

a  process  which  is  favoured  by  the  influence  of  sunlight. 

2.  From   methyl   alcohol,  CH4O  (a  substance  to   be  con- 
sidered  in   the   next   chapter,  when  we   shall   learn   that  the 
formula  is  conveniently  written  CH3  .  OH,  in  order  to  indicate 
the   way   in    which   the   alcohol   most   readily  reacts),  by  the 
action  of  various  compounds  containing  chlorine.      The  equa- 
tion is  simplest  in  the  case  when  HC1  gas  is  used  : 

CH3.OH    +    HC1    =    CH3C1     +     HaO, 
Methyl  alcohol.  Methyl  chloride. 

a  reaction  which  easily  occurs  when  HC1  is  passed  into 
boiling  methyl  alcohol,  to  which  some  zinc  chloride  (a  very 
hygroscopic  substance)  has  been  added. 

Methyl  chloride  is  a  gas  with  a  pleasant  smell,  fairly 
soluble  in  water,  and  pretty  easily  condensed  by  cold  or 
pressure  to  a  liquid.  It  is  used  commercially  in  the  manu- 
facture of  certain  aniline  dyes,  and  for  this  purpose  is  prepared 


CHLOROFORM 


from  a  by-product  of  the  beet-sugar  industry,  and  sold  com- 
pressed in  strong  steel  cylinders.  It  burns  with  a  green 
flame. 

Methene    Chloride,    CH2C12,   can    be    obtained    by   the 
further  action  of  chlorine  upon  methyl  chloride  : 

CHoCl  +  Cl,  -  CH9CL  +  HC1. 

O  A  A  A 

This  is  the  second  step  in  a  series  of  successive  substitutions 
of  the  hydrogen  atoms  by  chloride  ;  the  third  step  yields 

Chloroform,    CHC13,    which    is,    however,   more    readily 


prepared    by    a    complicated    reaction    where    ordinary 
alcohol,  C^H^O,  is  treated  with  bleaching  powder. 


ethyl 


FIG.  21. — Preparation  of  Chloroform  from  alcohol  and  bleaching  powder. 


EXPT.  7.  Mix  50  grams  of  bleaching  powder  with  250  c.c.  of  water, 
and  put  the  mixture  in  a  large  retort,  or  large  flask  fitted  to  a  Liebig's 
condenser  (see  figure)  ;  add  250  c.c.  of  methylated  spirit,  and  heat  the 
mixture  until  it  begins  to  boil.  Then  remove  the  burner,  and  allow  the 
reaction  to  proceed  by  itself.  Chloroform  and  water  are  condensed  in  the 
flask  B,  the  chloroform  sinking  to  the  bottom  of  the  water. 

The  mechanism  of  this  reaction  may  be  explained  now, 
though  it  will  scarcely  be  fully  understood  until  further 
acquaintance  with  the  subject  has  been  made.  The  bleaching 
powder  acts  both  as  an  oxidising  and  as  a  chlorinating  agent. 
In  the  first  capacity  it  removes  two  hydrogen  atoms  from  the 
ethyl  alcohol : 


METHYL  IODIDE  39 


CH3  .  CH2  .  OH  +  CaQa  =  CH3  .  CHO  +  H2O  +  CaQ2, 
Ethyl  alcohol.  Ethyl  aldehyde. 

but  the  product  CHg  .  CHO,  ethyl  aldehyde,  is  at  the  same 
time  chlorinated  and  converted  into  trichlorethyl  aldehyde 
or  chloral : 

CH3  .  CHO  +  3C12  =  CC13  .  CHO  +  3HC1, 
Aldehyde.  Chloral. 

while  the  chloral,  under  the  influence  of  the  lime  of  the 
bleaching  powder,  gives  chloroform  and  calcium  formate : 

2CC13.CHO    +    Ca(OH)2    -    2CHC1,     +     (HCO2)2Ca. 
Chloral.  Chloroform.  Calcium  formate. 

Chloroform  is  a  heavy  liquid  of  pleasant  ethereal  smell,  and  is 
much  used  in  surgery  on  account  of  the  property  which  its 
vapour  possesses  of  producing  insensibility  when  inhaled. 

Carbon  Tetrachloride,  CC14,  is  the  last  product  of  the 
substituting  action  of  chlorine  upon  methane  : 

CHC13  +  C12=CC14  +  HC1, 

and  is  obtained  as  a  pleasant  smelling  liquid  when  boiling 
chloroform  is  subjected  to  the  prolonged  action  of  a  stream  of 
chlorine  gas. 

Methyl  Iodide,  CH3I,  is  an  important  reagent  often  used 
in  the  synthesis  of  organic  compounds.  It  cannot  well  be 
prepared  by  the  direct  action  of  iodine  upon  methane,  but  is 
readily  obtained  by  the  action  of  iodine  and  phosphorus  upon 
methyl  alcohol  in  the  way  described  in  detail  for  making 
ethyl  iodide.  It  is  a  volatile  liquid  which  turns  brown  when 
exposed  to  light  ;  it  is  much  used  in  the  organic  laboratory. 

lodoform,  CHI3,  is  used  in  surgery  on  account  of  its 
marked  antiseptic  properties.  The  method  of  preparation  is 
analogous  to  that  of  chloroform,  but  instead  of  bleaching 
powder,  we  employ  iodine  together  with  some  alkali,  such  as 
sodium  hydrate  or  carbonate. 


40  ETHYL  CHLORIDE 


EXPT.  8.  Dissolve  10  grams  of  soda  crystals  in  50  c.c.  of  water,  and 
add  8  c.c.  of  methylated  spirit.  Heat  to  about  70°  C. ,  and  then  add 
gradually  5  grams  of  iodine.  lodoform  separates  out  as  a  yellow 
precipitate. 

lodoform  is  a  yellow  solid  with  a  characteristic  smell,  and 
is  slightly  soluble  in  hot  water,  from  which  it  crystallises  in 
lustrous  plates. 

Ethyl  Chloride,  C2Hr)Cl,  is  a  volatile  liquid  boiling  at 
about  12°  C.,  and  can  now  be  obtained  sealed  up  in  stout 
glass  tubes,  in  which  it  is  sold  for  use  as  a  local  anaesthetic 
in  minor  surgical  operations.  It  acts  in  this  way  by  virtue  of 
the  intense  cold  produced  by  its  rapid  evaporation  when  the 
liquid  is  allowed  to  spray  from  a  fine  opening  upon  the  part 
where  the  operation  is  to  be  done. 

It  is  prepared  by  the  action  of  HC1  gas  upon  ethyl  alcohol 
in  the  presence  of  zinc  chloride  : 

C2H5  .  OH  +  HC1  =  C2H5C1  +  H20, 

Ethyl  alcohol.  Ethyl  chloride. 

and  conversely  when  heated  under  pressure  with  water  (better 
with  solution  of  an  alkali)  ethyl  chloride  yields  ethyl  alcohol  : 

C2H5C1  +  H2O  =  C2H5  .  OH  +  HC1. 

Dichlor-ethane,  C.,H4CL,,  is  the  second  in  the  series  of 
substitution  products  obtained  by  the  action  of  chlorine  upon 
ethane  : 

C2H6     +C12=C2H5C1   +HC1, 
C2H5C1  +  C12  -  C,H4C12  +  HC1,  etc., 

but  we  here  meet  with  a  further  instance  of  isomerism,  and 
there  are  two  distinct  substances  possessing  the  formula 
C2H4C12.  In  one  of  these,  ethene  dichloride,  CHg  .  CHC12, 
both  chlorine  atoms  are  connected  with  the  same  carbon  atom, 
while  in  ethylene  dichloride,  CH2C1 .  CH9C1,  they  are  attached 
one  to  each  of  the  two  carbons. 

Ethene  Dichloride,  CH3 .  CHC12,  is  obtained  by  the 
action  of  chlorine  upon  ethyl  chloride,  as  a  rather  volatile 
liquid  with  a  smell  similar  to  that  of  chloroform. 

Ethylene  Dichloride,  CH2C1 .  CH2C1,  is  prepared  by  the 


ETHYL  BROMIDE 


direct  combination  of  ethylene  and  chlorine,  and  is  the  oily 
liquid  from  whose  formation  the  old  name  olefiant  gas  arose  : 

C2H4  +  C12    =    C2H4C12. 
Ethylene  Ethylene  dichloride. 

Ethyl  Bromide,  C9H5Br,  can  be  obtained  by  the  action  of 
bromine  upon  ethane  : 

C2H6+Br2  =  C2H5Br  +  HBr, 

Ethane.  Ethyl  bromide. 

but  more  readily  by  the  action  of  phosphorus  tribromide  (or 
phosphorus  and  bromine  together)  upon  ethyl  alcohol. 
Phosphorus  tribromide  reacts  with  water  thus  : 

PBr3  +  3H2O  =  P(OH)3  +  3HBr, 

that  is  to  say,  the  three  bromine  atoms  are  exchanged  for  the 
same  number  of  hydroxyls.  Ethyl  (or  any  other)  alcohol 
behaves  similarly  to  water  : 

PBr3  +  3C2H5OH  =  P(OH)3  +  3C2H5Br, 

yielding  phosphorous  acid  and  ethyl  bromide. 

Ethyl  bromide  is  a  volatile  liquid  with  a  pleasant .  ethereal 
smell. 

Just  as  with  dichlor-ethane,  C2H4C12,  there  are  also  two 
isomeric  substances  of  the  formula  C2H4Br2,  and  their  modes 
of  formation  are  precisely  similar  to  those  of  the  corresponding 
chloro-derivatives. 

Ethene  Dibromide,  CH3CHBr2,  is  obtained  by  the  action 
of  bromine  upon  ethyl  bromide  : 

C2H5Br  +  Br2  =  C2H4Br2  +  HBr. 
Ethene  bromide. 

Ethylene  Dibromide,  CH2Br .  CH2Br,  by  passing  a 
stream  of  ethylene  through  bromine  contained  in  a  series  of 
gas  washing  cylinders  : 

C2H4  +  Br2  =   C2H4Br2 

Ethylene  bromide. 


42  ETHYL  IODIDE 


Both  ethene  and  ethylene  bromides  are  heavy  liquids  with 
a  smell  similar  to  that  of  chloroform,  but  they  differ  markedly 
in  many  respects. 

Ethyl  Iodide,  C2H5I,  is  an  important  reagent  prepared  in 
a  way  precisely  similar  to  that  employed  for  ethyl  bromide, 
except  that  iodine  is  used  instead  of  bromine. 

EXPT.  9.  10  grams  of  red  phosphorus  and  60  c.c.  of  strong  alcohol 
("absolute"  alcohol  must  be  used  ;  rectified  spirits  of  wine  is  useless) 
are  placed  in  a  retort,  and  100  grams  of  iodine  added  little  by  little.  The 
mixture  is  allowed  to  stand  for  several  hours,  and  is  then  distilled  from  the 
water-bath  (see  figure).  If  the  alcohol  employed  has  been  weak,  fumes  of 


FIG.  22.— Preparation  of  Ethyl  Iodide. 

HI  will  be  evolved  in  torrents,  but  from  absolute  alcohol  only  traces  of 
HI  will  be  given  off.  The  methyl  iodide  is  condensed  in  the  Liebig's 
condenser,  and  collects  in  the  flask.  It  is  washed  with  caustic  soda 
solution  and  water,  then  dried  by  being  left  to  stand  in  a  highly-corked 
flask  over  lumps  of  fused  CaClo,  and  then  re-distilled. 

The  equation  for  the  reaction  is 

3C,HrpH  +  PI3=  3CaH,(I  +  HsPOa. 

Ethyl  alcohol.  Ethyl  iodide. 

Ethyl  iodide  is  a  colourless  liquid  with  an  ethereal  smell. 
It  boils  at  72°,  and  is  heavier  than  water,  sinking  to  the  bottom 
like  an  oil.  It  gradually  decomposes  when  exposed  to  light, 
and  the  liberated  iodine  colours  the  liquid  brown.  Both 
methyl  and  ethyl  iodides  are  largely  used  in  experimental 
organic  chemistry,  their  use  depending  on  the  great  mobility 


ETHYL  IODIDE  43 


of  the  iodine  contained  in  them.  This  iodine  is  readily 
exchanged  for  various  atoms  or  radicles  by  appropriate 
reactions,  and  many  new  compounds  have  been  obtained  by 
this  means. 


QUESTIONS  ON  CHAPTER  V 

1.  Describe  the  preparation  of  chloroform.      In  what  way  would  you 
attempt  to  prove  the  correctness  of  the  formula  CHCIs,  which  is  assigned 
to  it? 

2.  For  what  purposes  are  methyl  and   ethyl   iodides  employed,   and 
how  are  they  made  ? 

3.  Give  an  account  of  the  two  isomeric  substances  corresponding  to 
the  formula  C2H4Br2. 


CHAPTER    VI 
THE  ALCOHOLS 

THE  alcohols  form  a  homologous  series,  of  which  the  starting- 
point  is  methyl  alcohol,  CH4O.  Of  the  four  hydrogens  in  this 
molecule  one  is  distinguished  from  the  others  by  the  greater 
readiness  with  which  it  is  exchanged  for  other  atoms  or  radicals, 
while  the  fact  that  methyl  alcohol  may  easily  be  obtained  from 
or  converted  into  methyl  chloride,  CHgCl,  indicates  to  us  that 
the  formula  CH4O  may  better  be  written  CH3.OH.  This 
leads  us  to  consider  water,  H  .  OH,  as  the  inorganic  type  of 
the  alcohols,  and  it  will  be  useful  to  remember  that  there  exist 
many  points  of  resemblance  between  water  and  the  alcohols 
in  their  chemical  behaviour. 

Methyl  alcohol,  CHg.OH,  being  the  starting-point  of  the 
series,  the  next  member  is  ethyl  alcohol,  C9H6 .  OH,  and  so 
on  to  the  highest  known  member,  myricyl  alcohol,  C%H61 .  OH ; 
the  generic  formula  is  CWHOW+1  .  OH.  Chemically,  they  are 
characterised  by  the  presence  of  the  group  OH,  the  hydrogen 
of  which  may  easily  be  replaced  ( i )  by  sodium  or  potassium  : 

C2H5.OH  +  Na    -    C2H5.ONa    +    H, 

Sodium  ethylate. 
with  which  compare 

H.OH  +  Na    =       H.ONa       +     H  ; 
Sodium  hydrate. 

or  (2)  by  an  acid  residue  to  form  an  ethereal  salt  or  "ester," 
in  which  the  alkyl  group,  CwH2w+1,  takes  the  place  of  a  mono- 
valent  metallic  atom  in  an  inorganic  salt,  as  : 


CHAP,  vi  WOOD-SPIRIT  45 


(a)  C2H50  H  +  HO  N02  =  C2H5  .  ONO2  +  H2O, 
Ethyl  nitrate. 

(£)  CH3  .  OH  +  CH3  .  CO2H  =  CH3  .  CO2CHg  +  H2O, 

Methyl  acetate, 
with  which  compare 

(a)  NaOH  +  HO.N02    -      NaNO3      +    H2O, 
Sodium  nitrate. 

and       (V)  KOH  +  CH3.C02H  CH3 .  CO2K     +     H2O. 

Potassium  acetate. 

On  the  other  hand,  the  whole  group,  OH,  in  any  alcohol  is 
readily  driven  out  by  the  action  either  of  phosphorus  penta- 
chloride  or  of  HC1  (in  the  presence  of  some  hygroscopic  sub- 
stance such  as  ZnCl2),  and  its  place  taken  by  a  chlorine  atom : 

CH3OH  +  HC1  =  CH3C1     +      H2O 
Methyl  alcohol.  Methyl  chloride. 

C2H5OH  +  PC15  =  C2H5C1  +  HC1  +  POC13. 
Ethyl  alcohol.  Ethyl  chloride. 

Methyl  Alcohol,  CH3.  OH,  is  contained  in  wood-spirit,  a 
product  of  the  destructive  distillation  of  wood.  In  this  process, 
now  largely  carried  on  in  scientifically -constructed  retorts, 
there  are  obtained,  besides  the  charcoal  left  in  the  retorts,  the 
following  :  (a)  non- condensable  gases,  chiefly  CO,  H2,  and 
CH4,  which,  after  admixture  of  hydrocarbon  vapour,  may  be 
used  for  illuminating  purposes  ;  (b)  a  watery  liquid  containing 
acetic  acid,  methyl  alcohol,  and  many  other  substances  ;  and 
(c)  tar.  The  watery  distillate  (b)  is  distilled  anew  after  ad- 
dition of  enough  lime  to  retain  the  acetic  acid,  and  the  crude 
wood -spirit  thus  obtained,  after  some  further  treatment,  is 
saturated  with  CaCl2  and  heated  by  steam  to  100°  C.  The 
impurities  are  thus  driven  off,  and  a  residue  is  left,  consisting  of 
a  compound  of  CaCl2  with  methyl  alcohol.  This  is  mixed 
with  water,  when  the  methyl  alcohol  is  liberated  and  can  be 
recovered  by  distillation,  but  the  distillate  requires  to  be  again 
rectified  over  quicklime  in  order  to  free  it  from  water. 

Methyl  alcohol  is  a  light  colourless  mobile  liquid  with  a 


46  METHYL  ALCOHOL  CHAP. 

spirituous  odour.  When  ignited  it  burns  with  a  pale  blue 
flame.  The  pure  alcohol  is  used  in  the  manufacture  of  certain 
aniline  dyes,  and  for  this  purpose  it  should  be  as  free  as  pos- 
sible from  acetone,  a  substance  largely  present  in  crude  wood- 
spirit  ;  but  for  other  purposes,  such  as  for  dissolving  resins  in 
the  manufacture  of  varnish,  a  wood-spirit  rich  in  acetone  is 
desirable,  on  account  of  its  greater  solvent  power. 

The  presence  of  acetone  can  be  detected  and  its  amount  estimated  by 
means  of  its  property  of  yielding  iodoform  when  treated  with  iodine  and 
potash.  Pure  methyl  alcohol  itself  does  not  produce  iodoform,  whereas 
one  molecule  is  obtained  from  each  molecule  of  acetone  present. 

Methyl  alcohol  boils  at  66°.  It  is  considerably  lighter  than 
water,  but  mixes  with  it  readily. 

Chemically,  methyl  alcohol  is  the  type  of  a  primary  alcohol, 
that  is,  of  one  containing  the  group  —  CH2  .  OH.  Every  primary 
alcohol  when  oxidised  loses  first  two  atoms  of  hydrogen,  and 
gives  an  aldehyde  characterised  by  the  group  —  CHO,  which 
can  be  further  oxidised  to  the  group  -  COOH,  so  yielding  an 
acid.  In  this  particular  case  the  alcohol,  HCH2.  OH,  is  first 
oxidised  to  formaldehyde,  HCHO,  and  this  to  formic  acid, 
HCOOH,  by  treatment  with  appropriate  oxidising  agents. 

As  in  all  other  alcohols,  whether  primary  or  other,  the 
hydrogen  of  the  OH  group  can  be  readily  replaced  by  sodium 
or  potassium  : 


=   2CH3ONa    +    H2, 

Methyl  alcohol.  Sodium  methylate. 

and  the  hydroxyl  group,  as  a  whole,  is  substituted  by  chlorine 
by  the  action  of  PC15  : 

CH3.OH  +  PC15    -    CH;jCl    +    POC13  +  HC1, 
Methyl  alcohol.  Methyl  chloride. 

while,  on  the  other  hand,  the  synthesis  of  methyl  alcohol  can 
be  effected  by  heating  methyl  chloride  with  water  in  sealed 
tubes  to  a  temperature  of  120°  C.  : 

CH,C1  +  H  .  OH  =  CH3OH  +  HC1. 

Very  important  also  is  the  ability  of  methyl  alcohol  to  form 
ethereal  salts,  in  which  the  methyl  group  of  the  alcohol  plays 


VI 


ETHYL  ALCOHOL 


47 


the  same  part  as  the  metal  in  an  inorganic  salt.  These  are 
entirely  similar  to  those  derived  from  ethyl  alcohol,  which  will 
presently  be  considered  in  more  detail. 

Ethyl  Alcohol,  C2H5.OH,  is  prepared  on  a  very  large 
scale,  though  not  in  the  pure  state,  by  the  fermentation  of 
starch  or  sugar  contained  in  various  cereals  and  fruits.  The 
term  fermentation  is  applied  to  a  process  of  chemical  decom- 
position, depending  for  its  continuance  upon  the  influence  of 
some  "  ferment,"  which  yet  seems  to  take  no  part  in  the 
chemical  reaction,  and 
is  able  to  transform  a 
disproportionately  large 
amount  of  the  ferment- 
ing substance.  Fer- 
ments may  be  organised 
or  unorganised.  In  the 
first  case  they  are  living 
micro-organisms  whose 
activity  as  ferments  is 
connected  with  their  vital 
processes,  and  ceases 
with  their  death.  The 
unorganised  ferments 
are  definite  chemical 

Substances       called       en-         FlG   23._pure  Yeast  under  the  microscope. 

zymes,      but     no     satis- 

factory explanation  has  been  given  of  their  action. 

In  the  case  of  the  alcoholic  fermentation  of  sugar  we  are 
concerned  with  an  organised  ferment,  the  yeast  plant.  This  is 
a  minute  and  structurally  very  simple  plant,  which,  placed  in  a 
solution  of  sugar,  is  able  to  grow  and  multiply,  provided  the 
temperature  be  maintained  between  the  limits  of  5°  and  40° 
C.  ;  at  the  same  time  the  sugar  is  gradually  decomposed 
mainly  according  to  the  equation  : 


Glucose. 


Alcohol. 


but  there  is  always  produced  a  certain  amount  of  other  sub- 
stances, of  which  the  most  important  are  higher  alcohols  and 
their  ethereal  salts  ;  these  together  constitute  the  fusel  oil  of 


ALCOHOLIC  LIQUORS 


CHAP. 


the  crude  alcohol,  and  to  its  different  nature  are  due  both  the 
pleasant  flavour  of  good  wine  and  the  foul  taste  of  cheap 
spirit. 

EXPT.  10.  Dissolve  10  grams  of  sugar  in  200  c.c.  of  warm  water. 
Place  in  a  250  c.c.  flask  and  add  some  yeast.  Fit  the  flask  with  a  cork 
and  tube  to  pass  any  gas  evolved  through  lime-water. 

Arrange  a  parallel  experiment,  using  glucose  or  honey  instead  of  cane- 
sugar. 

Notice  that  fermentation  soon  begins  in  the  latter  case,  and  that  COo 
is  evolved.  The  cane-sugar  is  much  slower. 

The  most  important  alcoholic  beverages  may  be  classified 

as  follows  : — 

(«)   Beer   or   ale,   made   by  fermentation    of  the    sugar   in 

malted  cereals  (especially  barley),  and  containing  from  4  to  10 

per  cent  of  alcohol. 

The   malting  is  itself  a  fermentation  process.      The  active 

principle  is  the  diastase 
of  the  malt,  an  unor- 
ganised ferment  which 
converts  the  starch  of 
the  cereal  into  sugar. 

(b)  Wines,  made  by 
fermenting  the  sacchar- 
ine juice  of  ripe  fruit. 
No  ferment  is  artificially 
introduced,  as  in  the 
case  of  brewing  beer, 
but  micro  -  organisms 
floating  as  dust  in  the 
air  fall  into  the  must 
and  start  fermentation. 
Wines  contain  from  10 

FIG.  24.— Bloom  of  Grapes  under  the  microscope,  f        , 

showing  yeast  cells  at  A.  to     2O     per      CCllt     Ol      al- 

cohol. 

(<r)  Spirits  are  much  richer  in  alcohol  (30  per  cent  and  up- 
wards), and  are  made  by  distillation  of  the  weaker  spirituous 
beverages.  A  large  quantity  of  cheap  spirit  is  made  by 
fermentation  of  malted  potato- starch,  and  from  the  same 
source  the  bulk  of  the  alcohol  used  in  the  arts  and  manu- 
factures is  obtained. 


ALCOHOLOMETRY 


49 


Methylated  Spirit. —  In  order  that  the  high  price  of 
alcohol  due  to  the  heavy  duty  upon  it  may  not  seriously  inter- 
fere with  its  use  for  other  purposes  than  as  the  basis  of  intoxi- 
cating beverages,  the  so-called  methylated  spirit  is  allowed  to 
be  sold  duty  free.  This  is  a  mixture  of  alcohol  containing  20 
per  cent  of  water  with  substances  which  make  the  spirit  prac- 
tically undrinkable,  but  do  not  seriously  interfere  with  its  use 
for  other  purposes,  and  at  the  same  time  are  difficult  to 
remove.  The  present  regulations  order  that  certain  small 
proportions  of  wood-spirit  and  of  light  petroleum  shall  be  em- 
ployed as  the  methylating  mixture. 

Alcoholometry. — The  method  in  general  use  for  deter- 
mining the  percentage  of  alcohol  present  in  a  given  sample  of 
liquid  depends  upon  the  gradual  variation  in  the  specific 
gravity  of  mixtures  of  alcohol  and  water  as  the  proportion  of 
alcohol  is  altered.  The  following  short  table  illustrates  the 
way  in  which  the  specific  gravity  changes  : — 


Parts  by 

Parts  by 

weight  of 
alcohol  in  100 

Specific  gravity. 

weight  of 
alcohol  in  100 

Specific  gravity. 

of  mixture. 

of  mixture. 

0 

1.  000 

60 

.896 

IO 

.984 

70 

.872 

2O 

.972 

80 

.848 

30 

•958 

90 

.823 

40 

.940 

IOO 

•794 

50 

.918 

It  would,  of  course,  be  quite  incorrect  to  apply  this  table  to 
such  a  liquid  as  beer  or  wine,  in  which  other  substances  than 
water  and  alcohol  are  present,  and  influence  the  specific 
gravity.  What  is  done  in  such  cases  is  to  take  100  c.c.  of  the 
liquid,  distil  over  two-thirds  of  it,  and  make  up  the  distillate 
to  loo  c.c.  by  adding  water;  we  then  have  100  c.c.  of  liquid 
containing  all  the  alcohol  which  was  originally  present,  but 
freed  from  the  sugar  and  other  non-volatile  materials.  By 
taking  the  specific  gravity  of  this  distillate  we  find  at  once 

E 


5° 


PROOF-SPIRIT 


CHAP. 


from   the   table   what   percentage  of  alcohol  there  was   in  the 
beer  or  wine  taken. 

The  nomenclature  employed  in  this  country  for  stating  the 
results,  is  very  complicated.  The  standard  taken  is  proof- 
spirit^  originally  spirit  of  such  strength  that  when  poured 
over  gunpowder  and  set  fire  to,  it  was  just  able  to  ignite  the 
powder,  while  a  more  watery  spirit  failed  to  do  so.  The  present 
legal  definition  of  proof-spirit  is  that  it  should  be  of  the  specific 

I  2 

gravity — ,  which   corresponds   to  a  proportion  of  49.3    parts 

by  weight  of  pure  alcohol  in  100  of  the  mixture.     The  strength 
of  spirituous  liquors   is  generally  expressed  as  being  so  many 


FIG.  25. — Distillation  of  small  quantities. 

degrees  over  or  under  proof ;  thirty  degrees  over  proof  implies 
that  100  parts  of  the  spirit  contain  as  much  alcohol  as  130 
parts  of  proof-spirit. 

Pure  ethyl  alcohol,  absolute  alcohol,  is  obtained  from 
rectified  spirit  by  treatment  with  quicklime  and  subsequent 
distillation.  The  spirit  is  allowed  to  stand  over  lumps  of 
quicklime  for  several  hours  before  distillation,  and  even  then 
it  is  usually  necessary  to  repeat  the  process  before  the  alcohol 
is  entirely  freed  from  water.  Whether  this  is  the  case  can  be 
made  certain  by  shaking  some  anhydrous  copper  sulphate  (a 
white  powder  obtained  by  heating  the  crystallised  blue  salt 
for  several  hours  at  180°  C.)  with  the  alcohol,  when  the 
presence  of  even  a  trace  of  water  will  be  detected  by  the  white 
copper  sulphate  becoming  tinged  with  blue.  Anhydrous 


VI  SYNTHESIS  OF  ALCOHOL  51 

alcohol  is  very  hygroscopic,  and  must  be  preserved  in  well- 
stoppered  bottles. 

Pure  ethyl  alcohol  has  a  slight  pleasant  smell,  and  boils  at 
a  considerably  lower  temperature  than  water,  viz.  78-3°  C. 
Its  specific  gravity  is  .794  at  I5°C.  It  mixes  readily  with 
water,  and  can  be  used  as  a  solvent  for  many  substances  (resins 
and  other  organic  compounds)  which  are  insoluble  in  water. 

Other  methods  besides  that  of  fermentation  of  suga-  may 
be  used  for  the  preparation  of  ethyl  alcohol,  but  are  of 
theoretical  interest  only  ;  the  most  important  of  them  are  :  — 

I.  Ethylene,  C2H4,  is  absorbed  by  concentrated  sulphuric 
acid  with  formation  of  ethyl-sulphuric  acid  : 


and  this,  when  treated  with  hot  water,  is  decomposed  into 
alcohol  and  sulphuric  acid  : 

C2H5  .  HS04  +  H20  =  C2H5OH  +  H2SO4. 

As  ethylene  can  be  prepared  by  passing  a  mixture  of  acetylene  and 
hydrogen  over  platinum  sponge,  and  acetylene  has  been  made  by  direct 
union  of  carbon  and  hydrogen,  this  gives  a  way  by  which  it  would  Be 
possible  to  effect  the  synthesis  of  ethyl  alcohol  from  its  elements. 

II.  Ethyl  iodide,  bromide,  or  chloride,  when  heated  with 
water  (or  more  readily,  when  heated  with  solution  of  an 
alkali)  to  a  high  temperature,  yields  ethyl  alcohol, 

C2H5I  +  H,0  =  C2H5OH  +  HI. 

This  last  method  of  preparation  is  strong  evidence  for  the 
constitutional  formula,  CH3  .  CH2OH,  which  has  been  adopted; 
other  evidence  is  forthcoming  in  the  reactions  of  ethyl  alcohol, 
all  of  which  are  well  represented  by  this  formula.  Of  these 
reactions  the  following  only  will  be  mentioned  here  :  — 

I.  With  metallic  sodium  or  potassium,  an  alcoholate  is 
formed  and  hydrogen  is  evolved  : 

2C2H5  .  OH  +  2Na  =  2C2H5ONa  4-  H,. 
Sodium  ethylate. 

The  alcoholates  are  readily  oxidised,  and  are  decomposed  by  water 
with  formation  of  alcohol  and  a  hydrate  : 

C2H6ONa  +  H,O  =  Q,H5OH  +  NaOH. 


52  PROPYL  ALCOHOL 


II.  With  PC15,  or  HC1  in  presence  of  a  dehydrating  agent, 
ethyl  chloride  is  formed  : 

C2H5OH  +  HC1  =  C2H6C1  +  H2O. 

Zinc  chloride  may  be  used  as  the  dehydrating  agent.  Similar  reactions 
occur  with  HBr .  HI,  also  PBr3  and  PI3. 

III.  With  acids  the  alcohol  combines  to  form  ethereal  salts 
(seep.  55): 

C2H5OH  +  H2S04  =  C2H5  .  HS04  +  H2O. 

Alcohol  and  sulphuric  acid  yield  ethyl  hydrogen  sulphate  and 
water. 

Propyl  Alcohol,  C3H8O,  is  the  next  higher  homologue  of 
ethyl  alcohol,  and  is  the  lowest  member  of  the  series  for  which 
isomeric  forms  are  possible.  If  we  proceed  from  ethyl  alcohol, 
CH3 .  CH2OH,  by  substituting  a  methyl  group,  CH3,  for  a 
hydrogen  atom,  we  find  that  two  isomeric  alcohols  are  in- 
dicated for  the  formula  CQHCO  : 

t>          O 

CH3  .  CH2  .  OH  CH3  .  CH2  .  OH 
gives  gives 

*  CH        * 

CH3  .  CH2  .  CH2  .  OH  CH>CH  '  °H 

3 
Normal  propyl  alcohol.  Isopropyl  alcohol. 

and  both  of  these  isomers  are  well-known  substances. 

A  third  isomer,  CH3  .  CH2  .  O  .  CH3,  exists,  but  is  not  an  alcohol  ;  it  is 
methyl-ethyl  ether. 

Normal  propyl  alcohol  is  found  in  fusel  oil  in  considerable 
quantity,  and  can  also  be  prepared  synthetically  by  the  action 
of  water  or  potash  solution  upon  the  corresponding  iodide  : 

CH,  .  CH2  .  CH2I  +  H20  =  CH3  .  CH2  .  CH2OH  +  HI. 
Propyl  iodide.  Propyl  alcohol. 

Isopropyl  alcohol  does  not  occur  in  fusel  oil,  but  can  only 


vi      PRIMARY,   SECONDARY,  AND  TERTIARY  ALCOHOLS     53 

be  obtained  by  synthetical  methods,  as  by  the  action  of  water 
upon  isopropyl  iodide  : 

CH3.  CHI.  CH3+HaO  =  (CH3)2CHOH  +  HI. 

Both  these  alcohols  are  liquids  of  pleasant  smell  boiling  at 
a  somewhat  lower  temperature  than  water.  Chemically,  both 
exhibit  the  reactions  characteristic  of  alcohols  which  are 
mentioned  on  p.  51,  but  they  differ  markedly  from  one  another 
in  their  behaviour  towards  oxidising  agents.  Normal  propyl 
alcohol,  when  oxidised,  yields  first  an  aldehyde  and  then  an 
acid  (propionic)  : 

CH3.  CH2.  CH2OH ^CH3.  CH2.  CHO ^CH3.  CH2.  CO2H 

Primary  alcohol.  Aldehyde.  Acid. 

a  behaviour  completely  parallel  to  that  of  methyl  and  ethyl 
alcohols,  and  characteristic  of  all  alcohols  containing  the  group 
CH2 .  OH.  Such  alcohols  are  termed  primary  alcohols. 
Isopropyl  alcohol,  on  the  other  hand,  yields  first  a  ketone,  and 
this,  on  further  oxidation,  breaks  up  into  several  acids  con- 
taining a  smaller  number  of  carbon  atoms  in  the  molecule. 
This  behaviour  is  characteristic  of  secondary  alcohols, 
which  contain  the  group  CHOH  united  to  two  alkyl  groups  : 

CH3C09H 

(CH3)2  .  CHOH ^(CH3)2CO >       and  " 

H  .  CO2H 

Secondary  alcohol.  Ketone.  Lower  acids. 

The  next  alcohol  we  shall  consider,  butyl  alcohol,  will  furnish 
us  with  a  case  of  a  tertiary  alcohol.  Such  an  alcohol 
contains  the  group  C  .  OH  combined  with  three  alkyl  groups, 
and  on  oxidation  breaks  up  at  once  into  bodies  containing 
fewer  carbon  atoms  in  the  molecule  : 

(CH3)3  .  COH >-  bodies  with  fewer  carbon 

atoms  in  the  molecule. 
Tertiary  alcohol. 

Butyl  Alcohols,  C4H1QO,  occur  in  four  isomeric  forms. 
Their  derivation  from  the  two  propyl  alcohols  by  substitution 


54  BUTYL  ALCOHOLS  CHAP,  vi 

of   a  methyl    group    for  a  hydrogen    atom    is    shown    in  the 
following  table  : 

CH3  .  CH,  .  CH,OH  yields     (i.)  CH3  .  CH2  .  CH2  .  CH,OH 

Normal  butyl  alcohol. 

(ii.)  (CH3)2CH  .  CH2OH 
Isobutyl  alcohol. 

(iii.)  CH3  .  CH2 .  CH(CH3)  .  OH 
Secondary  butyl  alcohol. 

(CH3)2CHOH  yields    (iv.)  CH3  .  CH2  .  CH(CH3)  .  OH 

(v.)  (CH3)3COH 
Tertiary  butyl 
alcohol. 

but  of  these  (iii.)  and  (iv.)  are  identical,  so  that  the  full 
number  of  isomers  indicated  by  theory  is  four,  and  this  is  also 
the  number  actually  known.  Only  one  of  them  is  sufficiently 
important  to  be  further  mentioned.  Isobutyl  alcohol, 
(CH3)9CH  .  CH9OH,  can  be  separated  from  fusel  oil,  in  which 
it  is  present,  by  fractional  distillation.  It  is  a  liquid  boiling 
at  107°  C.,  and  possessing  the  characteristic  smell  of  fusel  oil. 
Amyl  Alcohol,  C5H12O. — For  this  alcohol  there  are  eight 
isomers  indicated  by  theory,  and  of  these  all  are  now  known. 
Two  of  these  are  largely  present  in  fusel  oil,  and  their  mixture 
is  the  ordinary  "  amyl  alcohol,"  a  liquid  of  unpleasant  smell, 
which  boils  at  about  130°  C.  It  is  obtained  from  fusel  oil  by 
fractional  distillation. 

QUESTIONS  ON  CHAPTER  VI 

1.  What  tests  would  you  apply  to  a  substance  given  to  you,  in  order 
to  discover  whether  it  is  an  alcohol  or  not? 

2.  How  is  methyl  alcohol  obtained  commercially?     Mention  important 
points   in  which  it  resembles,  and  others  in  which   it  differs   from,  ethyl 
alcohol. 

3.  Give  an  account   of  the    chief   chemical    changes   which    occur  in 
brewing  beer  from  barley.      How  would  you  determine  the  percentage  of 
alcohol  in  a  given  sample  of  beer  ? 

4.  What    are    the    characteristics    of    the    three    classes    of    alcohols, 
primary,  secondary,  and  tertiary? 

5.  Give  an  account  of  the  two  isomeric  alcohols  possessing  the  formula 
C3H80. 


CHAPTER    VII 
ETHEREAL  SALTS 
ETHERS— MERCAPTAN 

Ethereal  Salts. — As  has  been  already  mentioned,  the 
alcohols  are  able  to  combine  with  acids  somewhat  in  the  same 
way  as  the  inorganic  metallic  hydrates.  The  products  in  the 
case  of  the  latter  are  termed  salts,  while  those  formed  from 
the  alcohols  go  by  the  name  of  "  ethereal  salts  "  or  "  esters  "  : 

CH3.  OH-fHNO3     =     CH3NO3  +  H2O, 

Methyl  nitrate,  an  ethereal  salt. 
K.OH  +  HNO3    =    KNO3  +  H2O, 

Potassium  nitrate,  a  salt. 

There  are,  however,  several  differences  between  the  two 
classes  of  reactions,  of  which  the  most  important  is  that  the 
reaction  does  not  occur  so  readily  or  completely  with  the 
alcohol  as  with  the  base  ;  often,  especially  when  the  acid  is 
not  one  of  the  strongest,  it  is  necessaiy  to  employ  some 
dehydrating  agent  to  favour  the  reaction. 

The  reason  is  that  the  tendency  to  the  reversed  change,  such  as 
C2H5HS04  +  H20  =  C2H5OH  +  H2SO4, 

becomes  greater  as  the  quantity  of  water  present  increases.     By  combining 
this  water  with  some  hygroscopic  substance  its  effect  is  diminished. 

The  most  important  ethereal  salts  of  ethyl  alcohol  are 
perhaps  the  acetate  and  acid  sulphate. 


ETHYL  ACETATE 


Ethyl  Acetate,  CH3 .  CO2C2H5,  can  be  prepared  by 
heating  a  mixture  of  alcohol  and  acetic  acid  with  strong 
sulphuric  acid : 


C2H5OH 

Ethyl  alcohol. 


CH3.  CO2H 

Acetic  acid. 


CH3C02C2H5 

Ethyl  acetate. 


It  is  a  volatile  liquid  with  a  strong  fragrant  smell.  Its  forma- 
tion in  the  way  mentioned  is  employed  as  a  test  for  acetic 
acid  or  an  acetate. 


FIG.  26. — Saponification  of  ethyl  acetate  by  boiling  with  water  and  an  alkali ; 
the  reflux  condenser  prevents  loss  by  volatilisation. 


EXPT.  IT.  In  a  test  tube  mix  equal  volumes  of  spirits  of  wine  and 
strong  sulphuric  acid.  Add  some  pieces  of  a  solid  acetate,  and  notice  the 
fragrant  smell  of  ethyl  acetate  which  is  evolved  on  gently  heating  the 
mixture. 

Like  other  ethereal  salts,  ethyl  acetate  is  readily  split  up 
into  the  alcohol  and  acid  from  which  it  is  formed.  The  change 
may  be  accomplished  by  heating  with  water  in  sealed  tubes, 
or  more  readily  by  boiling  with  a  dilute  solution  of  an  alkali  : 


vii  SAPONIFICATION  57 


CH3C02C2H5  +  H20  =  CH3C02H  +  C2H5OH. 
Ethyl  acetate.  Acetic  acid.      Ethyl  alcohol. 

Changes  of  this  kind,  in  which  an  ethereal  salt  is  broken 
up  by  the  action  of  water  into  the  alcohol  and  acid  from  which 
it  is  formed,  are  often  spoken  of  as  cases  of  saponification. 
All  such  changes  occur  more  readily  when  an  alkali  or  an  acid 
is  present  in  the  water. 

Ethyl  acetate  is  used  in  the  artificial  preparation  of  per- 
fumes and  flavouring  essences.  Several  other  ethereal  salts, 
similar  in  composition,  are  also  used  for  these  purposes,  as 

Ethyl  butyrate,  C3H7CO9C2H5,  in  pine-apple  essence. 
Amyl  acetate,  CH3CO2C5Hn,  in  pear  essence. 

These  and  similar  compounds  also  constitute  the  bulk  of  the 
natural  essences  extracted  from  the  plants  themselves. 

Ethyl  Hydrogen  Sulphate,  C2H5HSO4,  is  formed  when 
alcohol  and  strong  sulphuric  acid  are  mixed.  It  can  be 
separated  from  unaltered  sulphuric  acid  by  means  of  its  barium 
salt,  which  is  soluble  in  water,  whereas  barium  sulphate  is 
insoluble.  Ethyl  hydrogen  sulphate  behaves  as  a  monobasic 
acid,  and  when  liberated  from  its  barium  salt,  can  only  be 
obtained  as  a  thick  uncrystallisable  syrup. 

Two  of  its  reactions  are  important  :  — 

(a)  When  heated  alone  it  splits  up  into  ethylene  and  sul- 
phuric acid  : 

C2H5HS04  =  C,H4  +  H2S04. 

In  this  case  a  larger  proportion  of  sulphuric  acid  is  used, 
and  the  temperature  of  the  reaction  is  higher. 

(b)  When  heated  with  alcohol  it  forms  ether  and  sulphuric 
acid  : 


C.jH5:HS04;  +  C2H50:H!  =  (C2H5)20  +  H2S04. 


In  this  case  alcohol   is  present  in  larger  quantity,  and  the 
decomposition  proceeds  at  a  lower  temperature. 


58  ETHYL  ETHER  CHAP. 


ETHER 

Ether  is  now  a  term  applied  to  a  whole  class  of  compounds, 
all  of  them  oxides  of  organic  radicles,  such  as  methyl  and 
ethyl.  Methyl  ether  is  (CH3)2O,  and  ethyl  ether  (C2H5)2O. 
This  latter  is  the  ordinary  "  sulphuric  ether  "  of  the  chemists, 
the  name  being  given  from  the  fact  that  sulphuric  acid  is  used 
in  its  manufacture,  although  the  substance  obtained  has  no 
sulphur  whatever  in  its  composition. 

Ethyl  Ether,  (C2H5)2O,  is  ordinarily  prepared  by  the  action 
of  ethyl-sulphuric  acid  upon  alcohol  : 

C2H5HS04  +  C2H5OH  ,=  (C2H5)20  +  H2SO4. 

EXPT.  12.  In  practice  a  mixture  of  alcohol  and  sulphuric  acid  (consist- 
ing, therefore,  largely  of  ethyl-sulphuric  acid)  is  heated  in  a  flask  to  about 
140°  C.,  and  then  a  slow  stream  of  alcohol  is  allowed  to  flow  into  the 
heated  liquid.  The  vapours  given  off  are  condensed,  and  yield  a  mixture 
of  water,  alcohol,  and  ether.  The  layer  of  ether  is  separated,  dried  over 
quicklime,  and  redistilled. 


FIG.  27. — Preparation  of  Ether. 

Ethyl  ether  is  a  colourless  mobile  liquid,  boiling  at  35°  C. 
Its  vapour  is  very  heavy,  and  also  readily  inflammable,  so  that 
care  must  be  exercised  in  working  with  ether  in  the  neighbour- 
hood of  a  flame.  The  smell  of  ether  is  pleasant,  but  when 
inhaled  in  quantity  the  vapour  produces  insensibility,  and  is 


MERCAPTAN  59 


used  as  an  anaesthetic  in  cases  where  chloroform  is  not  per- 
missible on  account  of  its  depressing  action  upon  the  heart. 
When  drunk  in  the  liquid  state  ether  produces  a  peculiar  kind 
of  short-lived  intoxication,  the  after  effects  of  which  are  very 
injurious  to  the  health. 

The  constitution  of  ether  is  not  evident  from  the  mode  of 
formation  given  above,  and  its  reactions  are  mostly  not  of  a 
character  to  throw  light  upon  this  point.  The  preparation 
from  ethyl  iodide  and  sodium  ethylate  (see  p.  51), 

C2H5I  +  C2H5ONa  =  C2H5  .  O  .  C2H5  +  Nal, 

is,  however,  strong  evidence  in  support  of  the  view  that  ordinary 
ether  is  oxide  of  ethyl. 


MERCAPTAN  AND  ETHYL  SULPHIDE 

A  large  number  of  organic  bodies  are  known  in  which  it 
seems  that  an  atom  of  sulphur  plays  the  part  of  an  atom  of 
oxygen  in  closely  related  compounds.  Such  are  the  mercaptans 
(e.g.  C2H5  .  SH),  which  correspond  to  the  alcohols  (C2H5.  OH), 
and  the  alkyl  sulphides^  e.g.  (C2H&)9S,  which  correspond  to  the 
ethers  (  (C2H5)2O). 

Ethyl  Mercaptan,  C2H5  .  SH,  is  formed  by  the  action  of 
potassium  sulphydrate,  KSH,  upon  ethyl  bromide  or  iodide  : 

C2H.Br+KSH  =  C2H5.  SH  +  KBr 
c.f.     C2H5Br  +  KOH  =  C2H5  .  OH  +  KBr. 

It  is  a  volatile  liquid  of  very  strong  and  unpleasant  odour. 
The  hydrogen  of  the  SH  group  is  more  readily  replaced  by 
metals  than  the  corresponding  H  atom  in  alcohols.  Not  only 
does  mercaptan  react  with  sodium  and  potassium,  but  also 
with  the  oxides  of  heavy  metals,  such  as  mercury : 

HgO  +  2C2H5  .  SH  =  (C2H5S)2Hg  +  H2O, 

(hence  the  origin  of  the  name  mercaptan,  mercurium  aptans), 
Ethyl  Sulphide,  (C2H5)9S,  can  be  prepared, 


60  ETHYL  SULPHIDE 


(i)  By  acting  on  potassium  sulphide,  K2S,  with  ethyl 
bromide  : 

K2S  +  2C2H5Br  =  (C2H5)2S  +  2KBr. 

When  a  solution  of  caustic  potash  is  saturated  with  H^S,  the  compound 
KHS  is  produced.  If  to  this  the  same  amount  as  was  originally  taken  of 
caustic  potash  solution  be  added,  K2S  is  formed  : 


and  KSH  +  KOH  =  K2S+H2O. 

(2)  By  treating    the    compound,    C2H5SK    (obtained  from 
mercaptan  by  action  of  potassium),  with  ethyl  bromide  or  iodide: 

C2H5  .  SK  +  C2H5Br  =  (C2H5)2S  +  KBr, 
with  which  compare  the  method  for  preparing  ether : 
C2H5  .  OK  +  C2H5Br  =  (C2H5)2O  +  KBr. 

Ethyl  sulphide,  like  nearly  all  volatile  organic  compounds 
which  contain  sulphur,  has  a  most  unpleasant  smell. 

QUESTIONS  ON  CHAPTER  VII 

1.  What  is  meant  by  an  "  ethereal  salt  "  ?     How  are  such  compounds 
prepared  ? 

2.  Mention  some  organic  compounds  of  the  class  of  ethereal  salts 
which  are  used  in  artificial  flavouring  essences. 

3.  What  two  substances  can  be  prepared  by  heating  ethyl  alcohol  with 
sulphuric   acid  ?     How  do  the  circumstances  of  the  reaction  need   to  be 
modified  in  the  two  cases. 

4.  Why  is  ether  regarded  as  ethyl  oxide  ?     What  sulphur-containing 
compound  resembles  it  in  composition,  and  how  is  it  prepared  ? 


CHAPTER   VIII 
ALDEHYDES  AND   KETONES 

The  Aldehydes  are  characterised  by  the  presence  of  the 
monovalent  group,  CHO,  whose  structure  is  represented  by  the 

formula  C^rJ  that  is  to  say,  the  general  behaviour  of  the 


aldehydes  is  best  represented  by  formulae  in  which  this  group 
is  connected  with  an  alkyl  group,  such  as  methyl  or  ethyl. 

The  aldehydes  occupy  an  intermediate  position  between  the 
acids  and  the  alcohols  by  whose  oxidation  they  are  produced  ; 
thus,  between  ethyl  alcohol,  CH3  .  CH2OH,  and  acetic  acid, 
CH3COOH,  stands  the  aldehyde  CH3.  CHO,  or  in  general  : 

R  .  CH2OH  -  H2  =  RCHO  ;  and  R  .  CHO  +  O  =  R  .  COOH  ; 

Alcohol.     -  ^-      Aldehyde.  -  ^-  Acid. 

and  the  names  of  the  aldehydes  are  best  chosen  so  as  to  denote 
their  connection  with  a  particular  acid,  the  one  into  which 
they  are  converted  by  addition  of  an  atom  of  oxygen.  Thus 
the  first  member  of  the  aldehyde  series,  H  .  CHO,  is  termed 
formaldehyde,  the  second  one,  CH3  .  CHO,  is  acetaldehyde, 
and  so  on. 

Formaldehyde,  H  .  CHO,  is  best  obtained  from  the  corre- 
sponding alcohol,  methyl  alcohol,  H  .  CH9OH,  by  oxidation  ; 
and  this  is  most  conveniently  effected  by  passing  warm  air 
saturated  with  the  vapour  of  methyl  alcohol  over  a  glowing 
copper  spiral. 

EXPT.  13.  In  the  centre  of  a  piece  of  combustion  tubing,  about  a  foot 
in  length,  place  a  two-inch  coil  of  copper  gauze.  Connect  one  end  of  the 


62  FORMALDEHYDE  CHAP. 

tube  through  two  gas-washing  bottles  (the  first  empty,  the  second  half  full 
of  water)  with  an  aspirator,  and  the  other  end  with  a  gas-washing  bottle 
containing  methyl  alcohol,  kept  at  about  50°  by  being  placed  in  a  beaker  of 
warm  water. 

Now  turn  on  the  water  tap  of  the  aspirator  until  a  vigorous  current  of 
vapour-laden  air  is  passing  over  the  copper  gauze.  Heat  this  gently  with 
a  Bunsen  burner  until  it  begins  to  glow,  when  it  will  continue  to  do  so 
without  any  further  use  of  the  burner  so  long  as  the  experiment  is  con- 
tinued. In  order  to  minimise  the  danger  of  cracking  the  glass  tube  when 
the  copper  spiral  suddenly  begins  to  glow,  it  is  well  to  support  the  spiral 
on  a  thin  piece  of  mica  or  of  asbestos  paper. 

In  this  way  are  obtained  only  mixtures  of  formaldehyde 
with  methyl  alcohol  and  water.  It  has  not  been  found  possible 
to  prepare  pure  formaldehyde,  H  .  CHO,  except  in  solution  or 
in  the  state  of  vapour.  When  the  solution  is  evaporated  or  the 
vapour  cooled,  a  solid  substance  is  obtained  of  the  same  com- 
position as  formaldehyde,  but  not  of  the  same  molecular  weight ; 
this  is  para-formaldehyde,  and  has  the  formula  (CH2O)^  where 
x  is  possibly  equal  to  3,  but  is  not  known  with  certainty.  Para- 
formaldehyde,  (CH9O)3  (?),  is  said  to  \>Q polymeric  with  form- 
aldehyde, CH9O,  as  the  two  substances  have  the  same  composi- 
tion, but  different  molecular  weights.  The  opposite  change  is 
easily  accomplished  by  vapourising  the  solid  para-formaldehyde 
when  a  vapour  whose  density  shows  it  to  be  made  up  of  the 
simple  molecules,  CH0O,  is  obtained  ;  but  on  cooling,  these 
again  gradually  unite  to  the  more  complex  molecules,  (CH2O)3. 

Beyond  its  tendency  to  polymerisation,  the  chief  charac- 
teristic of  formaldehyde  is  the  readiness  with  which  it  takes  up 
oxygen  from  other  substances  to  effect  the  change  into  formic 
acid  : 

H . CHO  +  O-H.  COOH; 
Formaldehyde.  Formic  acid. 

accordingly,  formaldehyde  is  a  strong  reducing  agent  ;  it 
reduces  in  the  cold  both  Fehling's  solution  and  solutions  of 
silver  salts. 

EXPT.  14.  Prepare  a  quantity  of  Fehling's  solution  by  dissolving  100 
grams  of  Rochelle  salt  (sodium  potassium  tartrate)  in  a  little  water,  add- 
ing 30  grams  of  NaOH  in  300  c.c.  of  water,  and  then  20  grams  of  crystal- 
lised CuSO4,  dissolved  in  about  100  c.c.  of  water  ;  mix  and  keep  in  a 
stoppered  bottle. 

Place  some  of  the  formaldehyde  solution  prepared  in  Expt.    13  in  a 


ACETALDEHYDE  63 


beaker,  and  add  Fehling's  solution  drop  by  drop.  Notice  that  its  dark 
blue  colour  is  discharged  and  a  light  red  precipitate  produced.  This  is 
CuaO,  formed  by  reduction  of  the  CuSO4  : 

2CuSO4  +  4KHO  +  H  .  CHO  =  HCO2H  +  Cu2O  +  2K2SO4  +  2H2O. 

EXPT.  15.  Dissolve  3  grams  AgNO3  in  a  mixture  of  20  c.c.  strongest 
ammonia  solution  (sp.  gr.  .88)  with  its  own  volume  of  water,  and  add  a 
solution  of  3  grams  NaOH  in  25  c.  c.  of  water.  Keep  in  a  small  stoppered 
bottle  in  a  dark  place. 

Take  some  of  this  silver  solution  in  a  test  tube,  and  add  a  few  drops  of 
the  formaldehyde  solution  ;  allow  to  stand  in  the  cold.  In  a  few  minutes 
a  brilliant  mirror  of  metallic  silver  will  be  deposited  on  the  sides  of  the 
test  tube. 

O3  +  H.>O  +  HCHO:  =  HCOOH  +  2HNO3  +  2Ag. 


Acetaldehyde,  CH3 .  CHO,  is  prepared  by  the  oxidation 
of  ethyl  alcohol  by  distillation  with  a  mixture  of  potassium 
bichromate  and  dilute  sulphuric  acid. 

EXPT.  16.  Place  in  a  flask  30  grams  K2Cr.,O7  (in  small  lumps)  and 
120  c.c.  water.  Mix  in  a  beaker  40  c.c.  methylated  spirit  and  25  c.c. 
strong  sulphuric  acid,  and  allow  to  cool.  Then  add  this  mixture  gradu- 
ally to  the  bichromate,  taking  care  to  keep  cool  by  running  water  over  the 
outside  of  the  flask. 

Heat  the  mixture  on  the  water-bath,  and  collect  the  distillate  in  a  re- 
ceiver kept  cold  by  ice.  The  impure  acetaldehyde  collected  can  be  purified 
partly  by  fractional  distillation,  and  finally  by  conversion  into  the  solid 
compound  which  it  forms  with  ammonia. 

Acetaldehyde  is  a  colourless  liquid,  boiling  at  21°  C.  and 
possessing  a  characteristic  smell.  Like  formaldehyde,  it  is  a 
strong  reducing  agent,  as  may  be  shown  by  experiments  similar 
to  Nos.  14  and  15.  It  further  resembles  the  lower  member 
of  the  aldehyde  series  in  the  readiness  with  which  it  poly- 
merises to  paraldehyde  (C2H4O)3.  Acetaldehyde  itself  is  a 
colourless  very  volatile  liquid  (B.P.  21°  C.)  with  a  pleasant 
smell,  but  on  standing  in  contact  with  even  a  trace  of  various 
substances — H2SO4,  HC1,  SO2,  etc. — it  changes  almost  en- 
tirely to  paraldehyde,  which  is  a  liquid  at  ordinary  temper- 
atures, but  solidifies  in  a  freezing  mixture,  boils  at  124°,  and 
gives  a  vapour  whose  density  corresponds  to  the  molecular 
formula.  (C2H4O)3.  Paraldehyde,  though  so  directly  obtained 


64  COMPOUNDS  OF  ACETALDEHYDE  CHAP. 

from  acetaldehyde,  is  not  itself  a  real  aldehyde  at  all.  This 
is  shown  by  its  whole  chemical  behaviour,  especially  by  the 
fact  that  it  does  not  reduce  metallic  silver  from  an  ammonia- 
cal  silver  solution,  and  leads  us  to  conclude  that  in  the 
formula  of  paraldehyde  the  group  -  CHO  no  longer  occurs. 
Paraldehyde  is  easily  reconverted  into  ordinary  acetaldehyde 
by  distillation  with  a  little  H^SO4. 

Metaldehyde  is  another  substance  of  the  formula  (C2H4O)3  obtained  by 
polymerisation  of  acetaldehyde  ;  it  is  isomeric  with  paraldehyde. 

Compounds  of  Acetaldehyde. — In  some  respects  acet- 
aldehyde is  more  typical  than  its  lower  homologue  of  the  group 
of  aldehydes,  and  we  have  therefore  delayed  till  now  the  con- 
sideration of  certain  reactions  exhibited  by  aldehydes  as  a 
class,  in  which  certain  substances,  such  as  NH3,  HCN,  etc., 
are  added  to  the  aldehyde  molecule. 

(a)  Acetaldehyde,  like  all  the  other  aldehydes  except 
H  .  CHO,  unites  directly  with  ammonia  to  form  a  compound 
of  the  type  R  .  CH(OH)(NH2)  : 

OH 
CH3.  CHO  +  NH3  =  CH8.  CH<^R  • 

This  particular  one  is  called  simply  aldehyde-ammonia,  and  is  formed 
as  a  white  crystalline  solid  when  dry  NH3  is  passed  into  an  ethereal  solu- 
tion of  aldehyde.  It  is  decomposed  by  dilute  acids  into  aldehyde  and 
ammonia. 

EXPT.  17.  Pass  NH3,  dried  by  quicklime,  into  a  solution  of  alde- 
hyde in  ether  ;  collect  on  a  filter  the  white  precipitate  produced,  and 
show  that  some  of  it  when  warmed  with  dilute  H2SO4  regenerates  alde- 
hyde. 

(V)  Addition  compounds  with  HCN  are  also  formed  by  the 
aldehydes,  thus 

/~\TT 

CH3.  CHO  +  HCN  =  CH3.  CH<^- 

(c)  Sodium  hydrogen  sulphite,  NaHSOy,  also  gives  addition 
products,  which  are  often  used  as  a  means  of  separating  and 
purifying  the  aldehydes.  The  following  equation  represents 
what  happens  in  the  case  of  acetaldehyde  : 

OH 
CH8.  CHO  +  NaHS03  =  CH3.  CH<gQjNa- 


CHLORAL  65 


Compounds  of  this  type  are  obtained  when  an  aldehyde  is  shaken  with 
a  saturated  solution  of  NaHSO3.  They  are  white  crystalline  solids,  soluble 
in  water,  and  decomposed  by  dilute  acids  with  regeneration  of  the  alde- 
hyde. 

Chloral  is  a  very  important  derivative  of  ordinary  alde- 
hyde ;  its  formula  is  CC13  .  CHO,  and  its  systematic  name 
trichlor-aldehyde. 

Chloral  is  prepared  by  passing  chlorine  into  alcohol  and 
decomposing  the  solid  crystalline  product  (a  compound  of 
chloral  and  alcohol)  with  sulphuric  acid.  The  reaction  may 
be  represented  as  occurring  in  two  parts  : 

(a)  The  alcohol  is  oxidised  to  aldehyde, 

CH3  .  CH2OH  +  C12  =  CH3 .  CHO  +  2HC1. 

Ethyl  alcohol.  Acetaldehyde. 

(b)  The   aldehyde    is   converted    into  trichlor-aldehyde   or 
chloral, 

CH3  .  CHO  +  3C12  =  CC13  .  CHO  +  sHCl. 
Acetaldehyde.  Chloral. 

It  is  a  liquid  with  a  penetrating  smell,  and  possesses  most  of 
the  properties  (reducing  power,  etc.)  characteristic  of  the  alde- 
hydes. It  is  decomposed  by  alkalies  with  production  of  chloro- 
form : 

CC13 .  CHO  +  KOH  =  CHC13  +  H  .  CO2K, 

Chloral.  Chloroform.     Potassium 

formate. 

hence  perhaps  the  well-known  narcotic  power  of  chloral. 

Chloral  Hydrate,  CC13 .  CHO  +  H2O,  is  a  compound  of 
chloral  with  water,  produced  by  direct  combination  of  the  two 
liquids.  It  is  a  crystalline  solid,  and  is  the  form  in  which 
chloral  is  usually  administered. 


KETONES 

The  ketones  are  a  series  of  compounds  resembling  in  many 
respects  the  aldehydes,  but  differing  in  others  ;  and  we  attempt 
to  represent  both  resemblances  and  differences  by  giving  to 
the  ketones  the  formula  R  .  CO  .  R,  closely  allied  to  the  alde- 
hyde formula  R.  CO  .  H. 


66  KETONES  CHAP. 

(i)  Just  as  the  aldehydes  are  obtained  by  carefully  gradu- 
ated oxidation  of  primary  alcohols, 

R  .  CH2OH  +  O  =  R  .  CO  .  H  +  H2O, 

Primary  alcohol.  Aldehyde. 

so  the  ketones  are  the  first  products  formed  by  the  oxidation 
of  secondary  alcohols,  that  is,  alcohols  in  which  the  group 
CH(OH)  is  combined  with  two  alkyl  groups  : 


.  OH  +  O  =     >CO  +  H20. 
Secondary  alcohol.  Ketone. 

(2)  Another  method  of  general  application  for  the  prepara- 
tion of  ketones  is  the  dry  distillation  of  the  calcium  salts  of 
fatty  acids  ;  thus  calcium  acetate  gives  acetone  or  di-methyl 
ketone  : 


CHgiCOO^ 

Calcium  acetate.  Acetone. 

(3)  A  third  method  of  considerable  importance  is  the  treatment  of 
acetyl  chloride  or  similar  compounds  with  zinc  methyl,  ethyl,  etc.  The 
reaction  may  be  represented  thus  : 


Acetyl  chloride.      Zinc  ethyl.         Methyl-ethyl 
ketone. 

The  ketones  resemble  the  aldehydes  in  their  power  of  form- 
ing addition  products  with  HCN,  and  with  NaHSO3.  They  do 
not  possess  the  same  energetic  reducing  power,  nor  do  they 
combine  with  ammonia  in  the  same  way  as  the  aldehydes. 

Acetone,  (CH3)2CO,  or  dimethyl  ketone  is  the  simplest 
ketone.  It  can  be  prepared  by  any  of  the  general  methods 
given  above,  the  one  generally  adopted  being  the  dry  distilla- 
tion of  calcium  acetate  : 

(CH3CO2)2Ca  =  (CH3)2CO  +  CaCO3. 

Acetone  is  also  found  amongst  the  products  of  the  dry  distilla- 
tion of  wood  (see  p.    45),   and  is  largely  obtained  from  that 


viii  ACETONE  67 

source.  It  is  used  as  a  solvent,  and  for  the  preparation  of 
iodoform  and  other  substances.  It  is  a  volatile  inflammable 
liquid  with  a  pleasant  smell. 

Oximes  and.  Hydrazones. — Special  importance  attaches  to  the  com- 
pounds which  aldehydes  and  ketones  form  with  hydroxylamine,  NH2(OH), 
and  phenylhydrazine,  C6H5NH  .  NH2.  In  these  oximes  and  hydrazones 
the  oxygen  of  the  CO  group  in  the  aldehyde  or  ketone  is  replaced  by  a 
divalent  residue,  thus  : 

(CH3)2CO  +  H2N  .  OH  =  (CH3)2C  :  N  .  OH  +  H2O 
Oxime. 

CH3COH  +  H2N  .  NHC6H5  =  (CH3)CH  :  N  .  NHC6H5  +  H2O. 

Hydrazone. 

The  importance  of  these  oximes  and  hydrazones  lies  in  their  great  utility 
as  a  means  of  characterising  the  various  aldehydes  and  ketones.  The 
hydrazones  especially  are  usually  crystalline  solids,  only  slightly  soluble  in 
the  ordinary  solvents,  and  are  therefore  much  more  easily  identified  than 
the  aldehydes  or  ketones  from  which  they  are  prepared. 


QUESTIONS  ON  CHAPTER  VIII 

1.  How  is  acetaldehyde  prepared?     Mention  its  chief  properties. 

2.  How  are  the  aldehydes  as  a  class  characterised  by  their  reactions, 
and  how  is  their  behaviour  represented  in  the  generic  formula  R  .  CHO  ? 

3.  What   is   the   relation  of  chloral   to   acetaldehyde  ?     Give   its  pre- 
paration and  properties. 

4.  What  bodies  are  formed  by  the  oxidation  of  (a)  ethyl  alcohol,  (3) 
aldehyde,  (c)  chloral? 

5.  Illustrate  the  chief  points  of  resemblance   and   difference   in  the 
chemical  behaviour  of  aldehyde  and  acetone. 


CHAPTER    IX 
THE   FATTY  ACIDS 

The  Fatty  Acids  form  an  important  homologous  series, 
some  higher  members  of  which  are  contained  in  all  natural 
fats.  The  lower  members  are  liquids  of  strongly  acid  char- 
acter and  sharp  penetrating  odour,  but  with  increasing 
molecular  weight  the  members  of  the  series  lose  their  solu- 
bility in  water,  and  with  it  their  acid  taste  and  power  of  turn- 
ing blue  litmus  red.  The  power  of  forming  salts  is,  however, 
unimpaired  even  in  the  highest  member  of  the  series  yet 
obtained. 

The  first  acid  of  the  series  is  formic  acid,  CH.2O2,  the  second 
acetic  acid,  C2H4O2.  The  general  formula  of  the  whole  series 
is  C^H2MO2,  but  this  is  better  written  CMH2M+1  .  CO2H,  to  in- 
dicate that  every  acid  of  the  series  contains  the  "carboxyl" 
group,  CO2H,  combined  with  a  hydrocarbon  residue  (or  "alkyl  " 
group),  such  as  methyl,  CHg,  ethyl,  C2H5,  etc.  Formic  acid  is 
then  written  H  .  CO2H,  acetic  acid  CH3 .  CO2H,  and  so  on. 

The  reasons  for  writing  the  formulae  in  this  way  will  be 
best  understood  if  we  consider  in  detail  the  case  of  acetic  acid  ; 
this  has  the  molecular  formula  C2H4O2.  Of  the  four  hydrogens 
only  one  can  be  replaced  by  metals,  i.e.  the  acid  is  monobasic, 
and  therefore  one  of  the  four  hydrogen  atoms  is  differently 
related  to  the  molecule  from  the  other  three.  Again  the  action 
of  phosphorus  pentachloride  on  acetic  acid  or  on  sodium 
acetate  yields  a  substance,  acetyl  chloride,  of  the  formula 
C2H3OC1 ;  that  is,  a  Cl  atom  takes  the  place  of  an  O  atom  and 
an  H  atom.  This  could  not  happen  unless  that  O  and  that  H 
were  connected  to  form  the  monovalent  hydroxyl  group  OH. 


CHAP.  IX  PREPARATION  OF  FATTY  ACIDS  69 

We  have  now  arrived  at  the  formula,  C2H3O  .  OH,  for  acetic 
acid.  The  next  question  is  whether  the  three  remaining  hydro- 
gen atoms  are  all  connected  to  the  same  carbon  atom  or  not. 
Acetic  acid  treated  with  chlorine  yields  a  derivative  trichlor- 
acetic  acid  of  the  formula  C0C13O  .  OH,  in  which  the  hydroxyl 
group  is  still  present,  and  the  other  three  hydrogens  are  re- 
placed by  chlorine.  Now  trichloracetic  acid  readily  yields 
chloroform  when  boiled  with  water  : 

C2C13O.OH    =    CHC13  +  CO2, 

Trichloracetic  acid.     Chloroform. 

showing  that  all  three  Cl  atoms,  and  therefore  the  three  hydrogen 
atoms,  whose  places  they  occupy,  are  connected  to  the  same 
carbon.  Hence  acetic  acid  contains  the  groups  CH3  and  OH, 
and  the  only  formula  in  agreement  with  these  experimental 
results  is  CH3  .  COOH. 

General  Methods  of  Preparation.  —  (i)  The  first 
method  is  one  which  also  furnishes  valuable  evidence  in  favour 
of  the  formula  C,zH2w+1 .  CO2H  for  the  series,  inasmuch  as  we 
start  in  each  case  from  a  substance,  C;,H2,Z+1  .  CN,  in  order  to 
prepare  the  corresponding  acid.  Such  an  alkyl  cyanide  is 
obtained  by  treating  the  iodide  of  the  same  radical  with  silver 
cyanide,  e.g.  : 

CH3I      +    AgCN    =    CH3.CN    +    Agl, 
Methyl  iodide.  Methyl  cyanide. 

and  when  heated  with  water  undergoes  a  reaction  of  the  fol- 
lowing type  : 

CH3.CN    +    2H2O  =  CH3.  CO2H  +  NH3. 
Methyl  cyanide.  Acetic  acid. 

Such  a  reaction  is  spoken  of  as  hydrolysis,  and  takes  place 
much  more  readily  when  a  dilute  mineral  acid  is  used  instead 
of  pure  water  ;  or  a  solution  of  an  alkali  may  be  employed. 

(2)  By  the  action  of  carbon  monoxide  on  the  sodium  com- 
pound of  an  alcohol,  e.g.  from  sodium  methylate  sodium  acetate 
is  obtained  : 

CH3  .  ONa  +  CO  =  CH3  .  COONa. 


70  FORMIC  ACID 


Similarly,  sodium  formate  may  be  obtained  from  sodium  hydrate: 
H  .  ONa  +  CO  =  H  .  COONa. 

This  method  is  of  theoretical  interest  only. 

3.  An  important  practical  method  is  the  oxidation  of  a 
primary  alcohol  containing  the  same  number  of  carbon  atoms 
as  the  acid  to  be  prepared  : 

CH3  .  CH2OH  +  O2  =  CH3  .  COOH  +  H2O. 
Ethyl  alcohol.  Acetic  acid. 

In  the  laboratory  a  mixture  of  potassium  bichromate  with 
dilute  sulphuric  acid  is  usually  employed  as  the  oxidising  agent  ; 
in  the  commercial  manufacture  of  acetic  acid  (vinegar)  the 
oxygen  of  the  air  is  utilised. 

In  this  method  the  group  CH2(OH)  is  oxidised  to  COOH. 
When  a  less  complete  oxidation  is  effected,  the  product  is  an 
aldehyde  containing  the  group  CHO  : 

R  .  CH,(OH) >  R  .  CHO >  R  .  COOH. 

Primary  alcohol.  Aldehyde.  Acid. 

Foimic  Acid,  H  .  CO2H,  may  be  prepared  by  any  of  the 
three  general  methods,  i.e.  : 

(i)  From  HCN,  hydrocyanic  acid,  by  heating  with  a  dilute 
mineral  acid  in  sealed  tubes  : 

HCN  +  2H2O  =  H  .  C02H  H-  NH3. 
Formic  acid. 

(2)  From     sodium     or    potassium    hydrate,    and    carbon 
monoxide  : 

NaOH  +  CO  =  H  .  COONa, 
Sodium  formate. 

a  reaction  which  occurs  with  great  readiness  when  moist  CO  is 
passed  over  porous  soda-lime  heated  to  about  200°  C. 

(3)  By  the  oxidation  of  methyl  alcohol  : 

HCH., .  OH  +  O,  =  HCOOH  +  H2O. 

Methyl  alcohol.  Formic  acid. 


ix  FORMIC  ACID  71 


Another  method  of  considerable  interest  in  connection  with  the  physio- 
logical chemistry  of  plants  by  which  formates  can  be  obtained  is  by  the 
reduction  of  CO2  in  the  presence  of  water.  Thus,  when  thin  slices  of 
metallic  potassium  are  exposed  to  a  moist  atmosphere  of  CO2  they  are 
gradually  converted  into  potassium  formate  and  carbonate  : 

2K  +  2CO2  +  H2O  =  H  .  CO2K  +  KHCO3. 

Possibly  this  reduction  to  formic  acid  is  the  first  step  in  the  transformation 
by  plants  of  CO2  into  sugar  and  starch. 

The  most  practically  useful  method  for  preparing  formic 
acid  is  by  the  decomposition  of  oxalic  acid.  This,  when  heated 
alone,  or  better  with  glycerine,  breaks  up  as  follows  : 

C2H2°4    =    H  '  CO2H    +    CO2' 
Oxalic  acid.      Formic  acid. 

A  mixture  of  equal  quantities  of  glycerine  and  crystallised  oxalic  acid  is 
heated  in  a  retort  until  no  more  CO2  is  evolved.  The  distillate  collected 
during  this  period  is  a  very  weak  formic  acid.  On  adding  more  oxalic 
acid,  and  again  heating,  a  stronger  acid  will  be  obtained,  but  the  acid  got 
in  this  way  never  contains  less  than  about  40  per  cent  of  water. 

Anhydrous  formic  acid  is  prepared  from  lead  formate  by 
the  action  of  hydrogen  sulphide.  The  lead  salt  is  easily  obtained 
from  any  (weak)  formic  acid.  It  is  dried  and  then  exposed  to 
a  stream  of  H2S  gas  in  a  tube  kept  warm  by  means  of  a 
steam  jacket.  The  anhydrous  acid  distils  over,  and  is  a 
colourless  liquid  with  an  acrid  odour  and  very  caustic  properties. 

Formic  acid  differs  from  the  other  members  of  the  series  in 
being  a  strong  reducing  agent.  It  reduces  solutions  of  silver 
and  mercury  salts  with  separation  of  the  metals.  When  heated 
with  strong  sulphuric  acid  it  is  decomposed  into  CO  and  water  : 

H.  CO2H  = 

The  Formates  of  the  alkali  metals  are  fairly  stable  sub- 
stances, which  crystallise  only  with  difficulty.  Those  of  the 
heavy  metals,  such  as  silver,  are  very  easily  decomposed  with 
separation  of  the  metal. 

Acetic  Acid,  CH3  .  CO2H,  can  be  obtained  by  any  of  the 
three  general  methods,  i.e.: 


72 


ACETIC  ACID 


(i)   From   CH.^  .  CN,   methyl    cyanide,    by  heating  with   a 
dilute  mineral  acid  or  a  dilute  alkali  : 


CH3.CN 

Methyl  cyanide. 


H3.  C02H  +  NH3. 
Acetic  acid. 


Methyl  cyanide,  CH3CN,  can  be  made  by  acting  with  methyl  iodide  on 
silver  cyanide  : 

CH3I  +  AgCN  =  CH3CN  +  Agl. 

(2)    From    sodium    or    potassium    methylate    and    carbon 
monoxide  : 


CH3.ONa    - 
Sodium  methylate. 

For  sodium  methylate,  see  p.  46. 


0  =  CH3.  COONa. 

Sodium  acetate. 


(3)   By  the  oxidation  of  ethyl  alcohol  : 


CH3CH2OH 
Ethyl  alcohol. 


H3  .  COOH 
Acetic  acid. 


H00. 


The  only  one  of  these  methods  employed  on  a  large  scale 
is  the  third.      In  the  preparation  of  vinegar  (which  is  a  dilute 

acetic  acid  flavoured  by 
minute  quantities  of 
other  substances)  the 
alcoholic  liquid,  whether 
wine,  diluted  brandy,  or 
merely  potato-spirit  and 
water,  is  exposed  to  the 
simultaneous  action  of 
the  air  (which  supplies 
the  oxygen),  and  of  the 
fermentative  influence  of 
a  particular  organism, 
the  mycoderma  aceti. 
The  process  is  carried 
on  most  rapidly  by  al- 
lowing the  alcoholic 
liquor  to  trickle  through 
tubs  filled  with  shavings, 
on  which  the  mycoderma  has  developed.  New  shavings  are 


FIG.  28. — The  mycodertna  aceti  or  "mother  of 
vinegar"  seen  under  the  microscope. 


ix  THE  ACETATES  73 

at  first  almost  inactive,  but  they  soon  become  coated  with  the 
organism,  and  the  oxidation  then  takes  place  readily. 

Large  quantities  of  acetic  acid  are  also  obtained  as  one  of 
the  products  of  the  destructive  distillation  of  wood.  The  acid  is 
separated  from  the  other  products,  chiefly  methyl  alcohol  and 
acetone,  by  neutralising  with  lime  and  distilling  the  alcohol  and 
acetone  from  the  calcium  acetate.  This  last  is  then  decomposed 
by  addition  of  sulphuric  acid,  and  the  acetic  acid  recovered  by 
distillation. 

Acetic  acid,  when  perfectly  free  from  water,  is  a  crystalline 
solid  which  melts  at  17°  C.  The  strongest  acetic  acid  of 
commerce  is  termed  "  glacial  acetic  acid,"  from  the  fact  that  it 
is  solid  in  moderately  cold  weather.  It  has  a  penetrating  acid 
smell,  and  acts  like  a  caustic  on  the  skin. 

The  salts  of  acetic  acid,  the  acetates,  are  prepared  by 
acting  with  the  acid  upon  the  oxide  or  carbonate  of  the  metal 
whose  acetate  is  required.  They  are  all  more  or  less  readily 
soluble  in  water,  and  crystallise  well. 

Sodium  Acetate,  NaC2H3O2,  crystallises  with  three  mole- 
cules of  water.  When  heated  above  1  00°  C.  the  water  of  crys- 
tallisation is  driven  off,  and  the  anhydrous  sodium  acetate  is 
left  as  an  amorphous  mass.  The  anhydrous  salt  is  used  in 
organic  synthesis  as  a  dehydrating  agent,  and  in  the  prepara- 
tion of  methane  : 

NaCHO  +  NaOH  =  CH   +  NaCO3. 


Ammonium  Acetate,  (NH4)C2H3O2,  is  a  deliquescent 
solid.  Its  solution  is  made  use  of  in  qualitative  analysis  for 
dissolving  lead  sulphate,  and  so  separating  it  from  mercuric 
sulphide,  with  which  it  may  be  mixed  in  the  course  of  working 
through  the  second  group  of  metals. 

When  strongly  heated,  ammonium  acetate  yields  acetamide 
and  water  : 

CH3COONH4  =  CH3CONH2+H2O. 

Calcium  Acetate,  Ca(C2H3O2)2,  is  used  for  preparing 
acetone  : 


CHgCO.O' 


74  PROPIONIC  ACID  CHAP. 

Lead  Acetate,  Pb(C2H3O2)2,  is  the  "  sugar  of  lead "  of 
commerce,  and  is  made  by  dissolving  litharge  in  acetic  acid. 
It  is  largely  used  in  the  manufacture  of  white-lead  (basic  lead 
carbonate)  and  chrome-yellow  (PbCrO4). 

Aluminium  Acetate  is  obtained  in  solution  when  calcium 
acetate  is  mixed  in  the  presence  of  water  with  aluminium 
sulphate.  The  solution  decomposes  on  evaporation  into  acetic 
acid  (which  escapes  as  vapour)  and  alumina  ;  hence  the  ex- 
tensive use  of  aluminium  acetate  as  a  mordant,  the  alumina 
combining  with  the  dye  to  form  an  insoluble  lake,  which  adheres 
firmly  to  the  fibre  of  the  cloth. 

As  tests  for  the  presence  of  acetic  acid  may  be  utilised 
either  the  dark  red  colour  of  the  solution  of  ferric  acetate 
(destroyed  on  boiling,  with  separation  of  a  basic  acetate  of  iron) 
formed  when  ferric  chloride  is  added  to  a  solution  of  an  acetate, 
or  the  formation  of  ethyl  acetate  with  its  characteristic  pleasant 
smell  when  an  acetate  is  heated  with  alcohol  and  concentrated 
sulphuric  acid. 

It  is,  however,  to  be  noted  that  these  tests  give  almost  identical  results 
with  any  of  the  acids  of  this  series.  To  distinguish  acetic  acid  from  its 
higher  homologues,  the  surest  plan  is  to  prepare  the  silver  salt  and 
determine  the  percentage  of  silver  which  it  contains. 

Propionic  Acid,  C2H5  .  CO2H,  may  be  prepared  by  any  of 
the  three  general  methods,  but  most  conveniently  by  the  third, 
starting  from  normal  propyl  alcohol  : 

C2H5  .  CH,OH  +  O2  -  C2H5  .  COOH  +  H2O. 
Propyl  alcohol.  Propionic  acid. 

The  constitution  of  propionic  acid  is  shown  by  this  method 
of  preparation,  as  also  by  that  from  ethyl  cyanide  by  hydrolysis : 

C2H5CN  +  2H2O  =  C2H5CO,H  +  NH3. 
Ethyl  cyanide.  Propionic  acid. 

Butyric  Acid,  C3H7  .  CO2H,  is  the  lowest  member  of  the 
series  for  which  isomeric  forms  are  theoretically  possible  or 
have  been  actually  obtained.  These  are  two  in  number,  viz.  : 

(i)   Normal  butyric  acid,  CH3CH2CH2CO2H. 
(ii)   Isobutyric  acid, 


xi  BUTYRIC  ACIDS  75 

Their  constitution  is  made  clear  by  their  synthetical  prepara- 
tion from  normal  propyl  iodide  and  isopropyl  iodide  respect- 
ively through  the  intermediary  of  the  cyanides  : 

(i)CH3CH2CH2I  -  ^CH3CH.2CH2CN  -  ^CH3CH2CH2CO2H 

Normal  propyl  iodide.     Normal  propyl  cyanide.         Normal  butyric  acid. 

(ii)  (CH3)2CHI  -  >•  (CH3)2CHCN  -  >-  (CH3)2CHCO2H 
Isopropyl  iodide.          Isopropyl  cyanide.  Isobutyric  acid. 

Normal  Butyric  Acid,  C3H7  .  CO2H,  is  present  in  butter 
in  the  form  of  glycerine  butyrate,  the  ethereal  salt  of  glycerine 
and  butyric  acid.  There  are,  however,  many  other  similar 
compounds  of  glycerine  contained  in  butter,  and  the  isolation 
of  the  butyric  acid  in  a  state  of  purity  is  a  matter  of  difficulty, 
and  the  acid  is  more  cheaply  and  easily  obtained  by  the  fer- 
mentation (under  the  influence  of  the  bacillus  subtilis}  of  sugar 
or  starch.  This  process  is  carried  out  on  a  fairly  large  scale, 
the  butyric  acid  being  converted  into  its  ethyl  salt,  which  is 
used  as  a  flavouring  under  the  name  of  essence  of  pine-apples. 
The  same  fermentation  of  starch  and  sugar  occurs  in  the 
human  stomach  in  certain  cases  of  deranged  digestion.  Start- 
ing from  glucose  (see  Chapter  XVIII),  the  change  produced  by 
the  fermentation  may  be  represented  by  the  equation  : 

C6H1206   =    C4H802    +    2C02  +  2H2. 
Glucose.  Butyric  acid. 

Butyric  acid  is  an  oily  liquid  with  an  unpleasant  rancid  smell. 
The  change  which  butter  undergoes  in  turning  rancid  may  be 
represented  (so  far  as  the  glycerine  butyrate  in  it  is  concerned) 
as  follows  : 


,)3  +  3H20  =  C3H5(OH)S  +  3C3Hr  .  CO2H, 
Glycerine  butyrate.  Glycerine.  Butyric  acid. 

and  it  is  to  the  presence  of  free  butyric  acid  in  rancid  butter 
that  its  characteristic  taste  and  smell  are  due. 

Isobutyric  Acid,  C3HrCO2H,  can  be  prepared  from  iso- 
propyl cyanide  (see  above),  and  resembles  the  normal  acid  in 
smell  and  taste,  though  differing  considerably  from  it  in  some 
other  physical  and  chemical  properties. 


76  STEARIC  ACID 


The  fifth  acid  of  the  series  is  valerianic  acid,  C4H9  .  CO.2H,  and  theory 
indicates  the  possible  existence  of  four  isomers,  all  of  which  have  been 
actually  prepared.  They  may  all  four  be  regarded  as  derivatives  of  acetic 
acid,  obtained  from  it  by  replacing  one  or  more  of  the  hydrogens  of  its 
methyl  group  by  alkyl  radicles.  They  are 

(i)   Propyl-acetic  acid,  C3H7  .  CH2CO2H. 
(ii)  Isopropyl-acetic  acid,  C3H7  .  CH2CO2H. 

~ 


(iii)  Ethyl-methyl-acetic  acid,  (T>CH  .  CO2H. 
(iv)  Trimethyl-acetic  acid  (CH3)3C  .  CO2H. 

Of  these  the  second  is  present  in  valerian  root,  while  all  of  them  may  be 
prepared  synthetically  by  utilising  some  one  or  other  of  the  general  methods 
given  on  p.  69  as  applicable  to  all  the  fatty  acids. 

The  higher  acids  are  not  of  great  importance  until  we  come  to  those 
with  sixteen  and  eighteen  atoms  of  carbon  in  the  molecule. 

Palmitic  Acid,  C15H31  .  CO<2H,  and  Stearic  Acid, 
C17H35  .  CO0H,  occur  in  combination  with  glycerine  as  the 
chief  constituents  of  animal  fats.  Glycerine  palmitate  is  also 
largely  present  in  most  vegetable  oils.  These  fats  and  oils 
serve  as  the  starting-point  of  three  important  manufactures  — 
those  of  soap,  glycerine,  and  stearic  acid.  In  making  soap 
the  fats  are  heated  with  caustic  potash  or  caustic  soda  solution, 
and  in  this  way  the  compounds  of  glycerine  with  various  fatty 
acids  which  are  contained  in  the  fat  are  "  saponified,"  that 
is,  are  converted  into  glycerine  and  the  potassium  or  sodium 
salts  of  the  acids.  If  we  consider  only  one  of  these  com- 
pounds, the  glycerine  stearate,  the  change  may  be  represented 
thus  : 

rococ17H35 

C3H  J  OCOC17H35  +  3NaOH  =  C3H5(OH)3  +  3C17H35COONa. 
|pCOCirHM 

Glycerine  stearate  Glycerine.  Sodium  stearate 

or  fat.  or  soap. 

The  other  compounds  present  undergo  similar  changes,  so  that 
there  is  obtained  along  with  glycerine  a  mixture  of  the  palmit- 
ates  and  stearates  of  sodium  or  potassium.  This  mixture  con- 
stitutes soap,  hard  soap  being  the  sodium  salts  and  soft  soap 
the  potassium  salts  of  the  acids  present  in  the  fats  employed. 
Formerly  it  was  the  practice  for  each  household  to  make  its 
own  soap,  but  the  tendency  of  modern  life  has  led  to  the 
manufacture  being  carried  on  almost  entirely  in  very  large 


IX  SOAP  77 

works.  The  process  is  of  the  simplest.  The  fat  or  oil  is 
heated  to  boiling  in  large  open  vats  along  with  the  solution  of 
soda  or  potash.  When  saponification  is  complete  common 
salt  is  added,  in  order  to  make  the  soap  separate  from  its 
solution  in  the  mixture  of  water  and  glycerine,  and  a  mass  of 
genuine  "  curd  soap  "  is  obtained  in  the  solid  state  above  the 
liquid  of  dilute  glycerine.  In  many  soap-boiling  establish- 
ments the  practice  is  adopted  of  allowing  the  mixture  of  soap, 
glycerine,  and  water,  which  is  the  immediate  result  of  the  boil- 
ing with  alkali,  to  solidify  together.  This  kind  of  soap  can 
obviously  be  sold  at  a  much  lower  rate  than  the  genuine  pro- 
duct, but  is  also  far  less  durable. 

In  working  up  the  fats  for  glycerine  and  stearic  acid  the 
process  is  again  one  of  "  saponification,"  that  is,  splitting  up 
an  ethereal  salt  of  glycerine  into  glycerine  and  the  acid  com- 
bined with  it  : 

Fat  +  water  =  glycerine  +  stearic,  etc.,  acid, 

and  is  now  most  largely  carried  on  by  subjecting  the  fat  to  the 
action  of  superheated  steam  in  the  presence  of  water  and  a 
small  proportion  of  lime.  The  product  is  freed  from  lime  by 
adding  the  proper  amount  of  sulphuric  acid  ;  and  in  this  way 
the  whole  of  the  acids  present  in  the  fat  are  obtained  in  the 
form  of  a  semi-solid  mass,  consisting  chiefly  of  palmitic  acid, 
C15Hpl .  CO2H,  stearic  acid,  C^H^  .  CO2H,  and  an  unsaturated 
acid  (see  p.  28),  oleic  acid,  C17H33.  CO^H.  Of  these  the  first 
two  are  solid,  while  the  last  is  liquid  at  ordinary  temperatures, 
and  can  be  removed  by  applying  hydraulic  pressure  to  the 
mixture  of  the  three  acids.  The  residue  is  the  "stearic  acid" 
of  commerce,  and  is  largely  employed  in  the  manufacture  of 
candles. 

The  isolation  of  pure  palmitic  or  stearic  acid  from  this 
mixture  is  a  matter  of  some  difficulty,  and  can  only  be  accom- 
plished by  a  tedious  process  of  fractional  precipitation  and 
crystallisation.  The  two  acids  are  very  similar  in  their  pro- 
perties, but  differ  in  their  melting  points. 

The  process  of  fractional  precipitation  is  carried  out  by  adding  to  the 
solution  of  the  two  acids  in  alcohol  a  quantity  of  magnesia,  only  sufficient 
to  combine  with  about  a  third  of  the  amount  of  acid  present.  The  pre- 


78  SOAP  CHAP,  ix 

cipitate  is  found  to  contain  a  much  larger  proportion  of  magnesium 
stearate  than  the  original  mixture  did  of  stearic  acid,  while  the  palmitic 
acid  is  almost  entirely  left  in  solution. 

The  salts  of  palmitic  and  stearic  acids  are  all  devoid  of  any 
tendency  to  crystallise.  A  mixture  of  the  sodium  salts  con- 
stitutes the  essential  portion  of  hard  soap,  while  soft  soap 
contains  the  potassium  salts.  The  lead  salts  are  also  im- 
portant ;  they  are  obtained  by  treating  fats  or  oils  with  latharge 
(lead  oxide)  and  water,  and  form  what  is  known  as  lead 
plaster. 


QUESTIONS  ON  CHAPTER  IX 

1.  The  analysis  of  acetic  acid  leads  to  the  empirical  formula  CHoO. 
Give  reasons  for  adopting  the  molecular  formula  C2H4O2. 

2.  Give  arguments  supporting  the  structural  formula  CHa  .  COgH  for 
acetic  acid. 

3.  Write  down  the  formulas  and  names  of  the  first  four  of  the  series  of 
fatty  acids.      Give  three  general  methods  which  (with  the  necessary  modi- 
fications) may  be  applied  to  the  preparation  of  each  of  them. 

4.  Mention  the  most  convenient  ways  of  obtaining  formic  and  acetic 
acids  in  quantity.      Point  out  any  important  difference  between  the  two 
homologous  acids. 

5.  Give  an  account  of  the  two  isomeric  butyric  acids,  their  constitution, 
preparation,  and  properties. 

6.  What  is  the  chemical  constitution  of  fats  ?     How  is  soap  made  from 
them? 


CHAPTER    X 
ACETYL  CHLORIDE  AND  ACETIC  ANHYDRIDE 

ACETIC  acid,  CH^COOH,  may  be  regarded  as  the  hydrate  of 
the  radicle  CH3CO  to  which  the  name  "acetyl"  is  given. 
The  chloride  and  oxide  of  acetyl  are  of  great  importance  as 
reagents  in  the  organic  laboratory. 

Acetyl  Chloride,  CH3COC1,  is  prepared  by  treating  acetic 
acid  with  phosphorus  trichloride,  and  distilling  the  mixture  : 

3CH3COOH  +  PC13  =  3CH3COC1      +      P(OH)3. 

Acetic  acid.  Acetyl  chloride.         Phosphorous  acid. 

It  is  thus  obtained  as  a  colourless  volatile  liquid,  which  fumes 
strongly  in  the  air,  and  combines  eagerly  with  water  to  form 
hydrochloric  and  acetic  acids  : 

CH3COiCl  +  H  OH  =  HC1  +  CH3COOH. 

Acetyl  chloride.  Acetic  acid. 

Exactly  parallel  is  the  action  of  acetyl  chloride  upon  organic 
alcohols  and  similar  bodies  which  contain  the  group  hydroxyl, 
OH.  Thus  with  ethyl  alcohol  it  gives  ethyl  acetate : 

CH3COC1    +    HOC2H5    =    HC1  +  CH3COOC2H5. 
Acetyl  chloride.     Ethyl  alcohol.  Ethyl  acetate. 

Acetic  Anhydride,  (CH8CO)2O,  acetyl  oxide,  is  obtained 
by  the  action  of  acetyl  chloride  upon  dry  sodium  acetate  : 


8o  ACETIC  ANHYDRIDE  CHAP. 

CHgCOONa    +    CH3COC1    ==    (CH3CO)2O    +    NaCl. 
Sodium  acetate.        Acetyl  chloride.     Acetic  anhydride. 

It  is  a  colourless  liquid  which  boils  at  136°  C.  It  is  heavier 
than  water,  sinking  to  the  bottom  as  an  oil,  but  reacts  gradu- 
ally with  it  forming  acetic  acid  : 

(CH3CO)20    +    H20  =  2CH3COOH. 

Acetic  anhydride.  Acetic  acid. 

This  change  takes  place  immediately  with  hot  water. 

Acetic  anhydride  acts  similarly  to  acetyl  chloride,  but  less 
energetically,  upon  substances  which  contain  the  hydroxyl 
group.  Both  reagents  replace  the  hydrogen  of  the  hydroxyl 
by  an  acetyl  group,  CH3CO,  and  both  are  much  used  for  the 
purpose  of  determining  the  number  of  hydroxyl  groups,  if  any, 
present  in  the  molecule  of  any  compound. 

Both  reagents  act  also  upon  the  SH  group  of  mercaptans, 
and  upon  the  NH2  or  NH  group  of  primary  or  secondary 
amines.  They  do  not  act  at  all  readily  upon  the  hydroxyl 
group  in  organic  acids. 

The  number  of  acetyl  groups  introduced  in  place  of 
hydrogen  atoms  by  the  action  of  acetyl  chloride  or  acetic 
anhydride  can  generally  be  discovered  by  analysis  (combus- 
tion) of  the  body  formed.  In  some  cases  it  is  better  to 
proceed  by  expelling  the  acetyl  groups  from  their  combina- 
tion by  boiling  the  substance  with  a  measured  volume  of 
standard  alkali  solution,  and  determining  the  amount  of 
alkali  left  in  excess  of  what  was  needed  to  neutralise  the 
liberated  acetic  acid.  The  method  may  be  exemplified  by 
a  simpler  case  than  any  to  which  it  would  in  practice  be 
applied  : 


CH3COOC2H5  +  NaOH  =  CH3COONa  +   C0Hr)OH. 

Ethyl  acetate.  Sodium  acetate.      Ethyl  alcohol. 

Each  molecule  of  alkali   spent  in  neutralising  liberated  acetic 
acid  represents  one  acetyl  group  in  the  body  examined. 

EXPT.  17.  In  a  small  strong  bottle  place  25  c.  c.  of  normal  sodium 
hydrate  solution  (40  grams  NaOH  to  the  litre),  and  then  run  in  i  c.  c.  of 
ethyl  acetate  from  a  i  c.c.  pipette.  Fit  the  bottle  immediately  with  an 
indiarubber  stopper,  firmly  tied  down.  Put  the  bottle  in  a  beaker  of 


AS  A  REAGENT  81 


water,  and  heat  the  water  to  boiling.  Allow  to  cool.  Then  wash  out 
the  contents  of  the  bottle,  and  determine  how  much  normal  sulphuric  acid 
(49  grams  H2SO4  to  the  litre)  is  required  to  neutralise  the  sodium 
hydrate  left  uncombined. 


QUESTIONS  ON  CHAPTER  X 

1.  Describe  how  you  would  prepare  acetic  anhydride. 

2.  Explain  the  use  of  acetyl  chloride  and  acetic  anhydride  in  investi- 
gating the  constitution  of  an  organic  compound. 

3.  Glycerine,  C3H5(OH)3,   forms  a  derivative,   C3H5(OC2H3O)3,  when 
treated  with   acetic  anhydride.      1.026  gram  of  this  glycerine  acetate  is 
heated  with  25  c.c.  of  normal  sodium  hydrate  until  complete  decomposition 
into  glycerine  and  acetic  acid  is  effected.      How  many  c.c.  of  normal  sul- 
phuric acid  would  be  required  to  neutralise  the  sodium   hydrate  left  in 
excess  ? 


CHAPTER    XI 
THE   AMINES 

THE  amines  have  for  their  inorganic  type  ammonia,  NH3, 
and  are  derived  from  it  by  replacement  of  the  hydrogen 
atoms  with  alkyl  groups.  If  only  one  of  the  three  hydrogens 
is  replaced  we  have  a  primary  amine,  such  as  methylamine, 
NH9CHg.  When  two  alkyl  groups  are  introduced  we  have 
a  secondary  amine,  such  as  dimethylamine,  NH(CH.,)0  ;  while 
in  a  tertiary  amine  all  three  hydrogens  are  replaced  as  in 
trimethylamine,  N(CH;3).,. 

The  power  possessed  by  ammonia  of  combining  with  acids 
to  form  neutral  bodies — the  ammonium  salts — is  retained  by 
its  alkyl  derivatives.  Indeed,  the  amines  with  which  we  are 
now  concerned,  and  in  which  methyl  and  ethyl  groups  take  the 
place  of  the  hydrogen  of  the  ammonia,  are  more  strongly 
basic  than  ammonia  itself,  while  resembling  it  very  markedly 
in  general  chemical  behaviour.  The  lower  members  of  the 
series  of  amines  are  gases  or  volatile  liquids  smelling  strongly 
of  ammonia,  but  differing  from  it  in  being  inflammable.  They 
combine  directly  with  acids  to  form  salts,  such  as  methylamine 
hydrochloride,  NH9(CH3)  .  HC1,  which  resemble  the  ammonium 
salts  in  many  respects,  but  differ  from  them  in  being  soluble 
in  alcohol. 

Very  important  are  the  double  salts  which  the  hydrochlorides  of  the 
amines  form  with  platinum  tetrachloride.  These  correspond  exactly  to  the 
ammonium  compound,  (NH^Cl^  .  PtCl4,  frequently  used  as  a  means  of  de- 
tecting and  estimating  ammonia.  Like  that  body,  they  are  decomposed  on 
ignition,  leaving  a  residue  of  metallic  platinum,  and  in  this  way  it  is  easy 


CHAP.  XI  PREPARATION  OF  AMINES  83 

to  determine  the  percentage  of  that  metal  in  any  of  these  double  salts. 
On  examining  the  formulae  of  these  compounds  : 

(NH3  .  HCl)2PtCl4,  (NH2CH3  .  HCl)2PtCl4, 

we  see  that  each  salt  contains  two  molecules  of  ammonia,  or  an  amine,  for 
each  atom  of  platinum,  and  we  may  write  the  formula  as  M2H2PtCl6, 
where  M  represents  the  amine.  The  atomic  weight  of  platinum  is  198, 
and  if  therefore  we  calculate  from  the  percentage  of  platinum  found  by 
ignition  how  many  parts  by  weight  of  the  double  salt  contain  198  parts  of 
that  metal,  we  have  the  molecular  weight  of  the  salt.  On  subtracting 
from  this  413  (2  +  198  +  213  :  H2PtCl6),  the  difference  is  twice  the  mole- 
cular weight  of  the  amine.  This  is  an  easy  and  accurate  method  of  deter- 
mining that  constant,  often  the  best  way  of  identifying  an  unknown 
member  of  the  amine  series. 

Example.  The  platinum  double  salt  of  an  amine  gave  the  following 
results  on  ignition  :  .1935  gram  yielded  .077  gram  platinum.  Calculate 
the  molecular  weight  of  the  amine. 

These  numbers  show  that    198   parts  of  platinum  are  contained   in 

198  x  —-—483.3  parts  of  the  double  salt.     Therefore 
M  =  £(  483.3  -4i3). 


and  the  amine  is  either  dimethylamine,  NH(CH3)2,  or  ethylamine, 
NH.2C2H5,  both  of  which  have  the  molecular  weight  35.  To  distinguish 
between  these  two  isomers  would  require  further  experiment.  See  p.  84. 

General  Method  of  Preparation  of  the  Amines. 
—  The  chief  method  was  discovered  by  Hofmann,  and  consists 
in  heating  together  ammonia  (in  alcoholic  solution)  and  an 
alkyl  iodide  or  bromide.  By  this  reaction,  which  requires  a 
temperature  of  about  100°  C.  and  the  use  of  sealed  glass 
tubes  such  as  are  employed  in  Carius's  method  of  analysis 
(see  p.  9),  a  mixture  of  the  iodides  of  primary,  secondary, 
and  tertiary  amines  is  obtained,  and  the  following  equations 
represent  the  changes  which  occur  : 


(1)  NH3  +  CH3I      =      NH2CH8.HI. 

Methyl-ammonium  iodide. 

(2)  NH8  +  2CH3I    =    NH(CH3)2.  HI  +  HI. 

Dimethyl-ammonium  iodide. 


(3)   NH3  +  3CH3I  "=    N(CH3)3.  HI  +  2HI. 
Trimethyl-ammonium  iodide. 


84  PRIMARY  AMINES  CHAP. 

At  the  same  time  there  is  produced  some  amount  of  a  com- 
pound, N(CH3)4I,  belonging  to  the  class  of  quaternary  am- 
monium salts  : 


(4)  NH3  +  4CH3I  N(CH3)4I  +  3HI. 

Tetra-methyl-ammonium  iodide. 

The  proportions  in  which  these  four  substances  are  produced 
depend  on  the  particular  alkyl  iodide  employed.  In  any  case 
their  separation  is  a  matter  of  considerable  labour  and  diffi- 
culty. 

The  quaternary  ammonium  salt  (such  as  N(CH3)4I)  is  not  decomposed 
on  boiling  with  soda  or  potash,  and  is  thus  easily  separated  from  the  three 
amines,  of  which  a  mixture  is  liberated  on  treating  with  alkali  the  pro- 
duct obtained  by  Hofmann's  method.  The  tertiary  amine,  N(CH3)3,  is 
alone  left  unacted  upon  when  this  mixture  is  treated  with  nitrous  acid, 
while  the  secondary  amine  is  converted  into  a  nitrosamine  : 

NH(CH3)2   +    HNO2     =      (CH3).2N  .  NO      +      H2O, 
Dimethylamine.  Dimethyl-nitrosamine. 

and  the  primary  amine  into  an  alcohol  : 

NH2CH3+HN02     =      CH3.OH    +    N2  +  H2O. 

Methylamine.  Methyl  alcohol. 

It  is  not  very  difficult  thus  to  isolate  the  tertiary  amine,  and  from  the 
nitrosamine  the  secondary  base  can  be  recovered.  The  primary  amine  is, 
however,  lost,  but  there  are  other  much  more  convenient  ways  for  the 
preparation  of  the  primary  amines,  so  that  this  disadvantage  is  not  very 
serious. 

The  Primary  Amines  of  the  type  R.NH.,,  where  R 
represents  an  alkyl  group  (CHg,  C2H5,  etc.),  are  more  strongly 
basic  than  ammonia  itself.  They  are  produced  in  Hofmann's 
general  reaction,  but  are  difficult  to  separate  from  the  resulting 
mixture  of  ammonium  salts.  Several  methods  are  known  by 
which  primary  amines  can  be  obtained  in  a  state  of  purity,  and 
the  most  important  of  these  is  also  due  to  Hofmann.  The 
amide  (see  p.  88)  of  an  organic  acid,  on  treatment  with 
bromine  and  potash,  undergoes  a  peculiar  kind  of  partial 
oxidation  : 

RCONH,  +  O  =  R.  NH2  +  CO2, 
Amide.  Amine. 


XI  SECONDARY  AND  TERTIARY  AMINES  85 

and  the  primary  amine  containing  one  carbon  atom  less  in  the 
molecule  is  obtained  perfectly  free  from  secondary  or  tertiary 
base. 

In  reality  an  intermediate  product  R  .  CONHBr  is  first  formed  : 

R.  CONH^j  +  Bn.+  KOH^RCONHBr+KBr+HiA 
and  is  then  decomposed  by  more  potash  : 

R  .  CONHBr  +  sKOH  =  RNH2  +  K2CO3  +  KBr  +  H.2O. 

The  primary  amines  react  very  readily  with  many  reagents. 
We  can  only  refer  here  to  the  formation  of  alcohols  from  them 
by  the  action  of  nitrous  acid  : 


RNH2     +     HNO2-R.  O 
Primary  amine.  Alcohol. 

The  Secondary  Amines,  R2NH,  are  best  distinguished 
from  primary  and  tertiary  amines  by  the  formation  of  nitros- 
amines,  R2N  .  NO,  on  treatment  with  nitrous  acid  : 

R2NH    +    HNO2  =  R2N.NO  +  H2O. 

Secondary  amine.  Nitrosamine. 

These  nitrosamines  are  mostly  oils,  insoluble  in  water,  which 
regenerate  the  amine  when  boiled  with  concentrated  hydro- 
chloric acid  : 

R2N  .  NO  +  HC1  =  R2NH  +  NOC1. 

The  Tertiary  Amines,  R3N,  are  still  more  strongly 
basic  than  either  primary  or  secondary  amines  containing  the 
same  alkyl  groups.  They  are  unacted  upon  by  many  reagents 
which  readily  affect  the  other  two  classes  of  amines,  such  as 
nitrous  acid,  acetic  anhydride,  etc.,  and  can  thus  be  easily  dis- 
tinguished or  separated  from  them. 

Methylamine,  NH0CH3,  is  a  colourless  gas,  very  soluble 
in  water,  and  possessing  a  strong  smell  of  ammonia.  It  is 
combustible.  The  most  convenient  method  of  preparing  it  in 
the  laboratory  is  by  the  action  of  bromine  and  potash  on 
acetamide,  or  a  reaction  represented  by  the  following  equa- 
tion : 

CH3CONH2  +  KOH  +  Br2  =  CH3NH2  +  2KBr  +  K2CO3 
Acetamide.  Methylamine. 


86  METHYLAMINE 


A  substance,  CHaCONHBr,  is  formed  as  an  intermediate  product.  For 
experimental  details  a  book  on  Organic  Preparations  should  be  con- 
sulted. 

Methylamine  is  strongly  alkaline,  and  combines  readily  with 
acids.  Its  hydrochloride,  NH2CH3.HC1,  is  very  soluble 
in  water.  The  platinum  double  salt  has  the  formula 
(NH2CH3.  HCl)2PtCl4,  and  is  only  slightly  soluble  in  water, 
from  which  it  crystallises  in  minute  hexagonal  plates,  whose 
appearance  under  the  microscope  is  very  characteristic. 

Dimethylamine,  NH(CH3)2,  is  a  volatile  liquid  boiling 
at  7°.  Its  odour  is  at  once  somewhat  fishy  and  strongly 
ammoniacal.  It  is  present  in  herring-brine,  and  in  large 
quantity  in  a  by-product  of  the  manufacture  of  beet-sugar. 

Dimethylamine  is  most  conveniently  made  on  a  small  scale  from  a 
derivative  of  aniline.  This  substance,  which  is  to  be  described  more  fully 
in  Part  II.,  is  a  primary  amine  of  the  formula  C6H5.NH2,  and  can,  by  treat- 
ment with  methyl  chloride,  be  converted  into  C6H5  .  N(CH3)o,  dimethyl- 
aniline.  From  this,  by  a  peculiar  reaction  which  we  cannot  here  describe 
further,  it  is  possible  to  prepare  pure  dimethylamine. 

Trimethylamine,  N(CH3)3,  in  the  undiluted  state  smells 
of  ammonia,  but  when  largely  mixed  with  air  (possibly  owing 
to  some  kind  of  oxidation)  has  a  strong  odour  of  rotten  fish. 
It  is  present  in  herring-brine,  as  also  in  the  by-product,  already 
referred  to,  of  the  beet-sugar  manufacture.  This  product  is 
obtained  by  the  dry  distillation  of  beet-root  molasses,  and  con- 
tains all  three  methylamines  but  dimethylamine  in  largest 
quantity.  This  mixture  has  been  largely  used  in  the  manufac- 
ture of  methyl  chloride,  as  all  the  methylamines  when  heated 
with  concentrated  HC1  are  converted  into  ammonia  with 
separation  of  methyl  chloride  : 

N(CH3)3  .  HC1  +  2HC1  -  NH3  +  3CH3C1, 
NH(CH3)2.  HC1  +  HC1  =  NH3  +  2CH3C1, 
NH2CH3.  HC1  =  NH3  +  CH3C1. 

Tetramethyl- ammonium  Iodide,  N(CH3)4I,  is  the 
chief  product  of  the  action  of  NH3  on  CH3I.  The  radicle 
N(CH3)4  is  so  strongly  electro-positive  that  the  compound 
N(CH3)4I  is  not  decomposed  by  potash  or  soda,  but  on  treating 


XI  ETHYLAMINE  87 

it  with  moist  silver  oxide,  the  ammonium  hydrate  N(CH3)4OH 
is  obtained  : 

2N(CH3)4I  +  Ag2O  -f  H2O  -  2N(CH3)4OH  +  2AgI. 

The  solution  of  this  hydrate  is  as  strongly  alkaline  as  a 
solution  of  potash  or  soda,  and  it  is  interesting  to  notice  the 
more  and  more  marked  alkaline  character  of  the  compounds 

NH3,  NH2CHy,  NH(CH3)2,  N(CH3)3,  N(CH,)4OH, 

as  the  number  of  alkyl  groups  attached  to  the  nitrogen  atom  is 
increased. 

Ethylamine,  NH2C2H5,  is  obtained  along  with  di-  and  tri- 
ethylamines  by  heating  together  in  sealed  tubes  ethyl  iodide 
and  alcoholic  ammonia.  Like  other  primary  amines,  it  is 
decomposed  by  nitrous  acid  : 

NH2C2H5  +  HNO2  =  C2H5OH  +  N2  +  H2O, 

whereas   Diethylamine,    NH(C2H5)2,   forms    a    nitrosamine, 
(C2H5)2N  .  NO,  and  Triethylamine  is  unaltered. 


QUESTIONS  ON  CHAPTER  XI 

1.  What  substances  are  formed  when  ethyl  iodide  is  heated  in  sealed 
tubes  with  an  alcoholic  solution  of  ammonia? 

2.  How   can    you   distinguish   the   three   classes   of   amines,    primary, 
secondary,  and  tertiary? 

3.  How  would  you  prepare  mono-ethylamine  ?     What   is   the  action 
upon  it  of  hydrochloric  and  of  nitrous  acids. 

4.  The  platinum  double  salt  of  an  amine  gave  the  following  result 
upon  analysis  :   .2055  gram  of  the  double  salt  left  .0680  gram  of  platinum 
upon  ignition.     Calculate  the  molecular  weight  of  the  amine. 


CHAPTER    XII 
THE  AMIDES  AND  AMIDO-ACIDS 

The  Amides,  like  the  amines,  are  derived  from  ammonia  ; 
but  whereas  in  the  amines  the  hydrogen  of  the  NH3  is  re- 
placed by  an  alcohol  radicle  (or  "  alkyl  "  group),  such  as 
methyl,  CH3,  or  ethyl,  C2H5,  in  the  amides  the  substituting 
group  is  an  acid  radicle. 

These  acid  radicles  are  those  which  yield  acids  when  com- 
bined with  the  hydroxyl  group  OH  (see  p.  68),  the  radicle  of 
acetic  acid  being  CH3  .  CO,  acetyl,  that  of  propionic  acid 
being  C2H5  .  CO,  propionyl.  Ace/-a.m\de.  is  the  name  given 
to  the  amide  CHSCONH2,  in  which  one  of  the  three  hydrogens 
in  the  ammonia  has  been  replaced  by  the  acetyl  group,  whilst 
propion-a.m\&e  is  the  name  used  for  C2H5CONH9. 

Methods  of  Formation.  —  (i)  The  first  of  these  is  by  the 
action  of  ammonia  upon  the  chloride  of  the  acid  radicle  ;  e.g. 
acetyl  chloride  yields  acetamide  : 


CH3COC1    +    2NH3  =  CH3CONH2  +  NH4C1. 

Acetyl  chloride.  Acetamide. 

This  is  analogous  to  the  preparation  of  the  amines  from 
alkyl  iodides  (or  chlorides)  and  ammonia  ;  but  the  reaction 
occurs  far  more  readily  with  the  acid  chlorides,  so  that  it  is 
often  necessary  to  employ  means  to  moderate  the  violence  of 
the  action. 

(2)  The  second  method  only  differs  from  the  first  in  the 
use  of  an  ethereal  salt  of  the  acid  instead  of  the  acid  chloride. 


CHAP,  xii  ACETAMIDE 


Thus  ethyl  acetate  when  heated  with  ammonia  gives  acetamide 
and  ethyl  alcohol : 


CH3CO;OEt  +  H:NH2  =  CH3CONH2  +  EtOH. 

Ethyl  acetate.  Acetamide. 

This  method  in  many  cases  requires  the  action  of  a  high 
temperature  (150°  C.)  for  several  hours,  and  involves  therefore 
the  use  of  closed  vessels  which  can  stand  very  considerable 
pressure.  On  the  small  scale,  sealed  glass  tubes  similar  to 
those  used  in  Carius's  method  of  analysis  (p.  9)  are  employed, 
but  unless  very  well  made,  these  cannot  stand  the  pressure 
of  the  strong  aqueous  ammonia  at  150°  C. 

(3)  The  third  method  consists  in  heating  strongly  (230°  C.) 
the  ammonium  salt  of  the  acid,  when  it  loses  water  and  is 
converted  into  the  amide  : 

CH3COONH4  =    CH3CONH2+H20. 
Ammonium  acetate.  Acetamide. 

Here  again  it  is  generally  necessary  to  heat  in  closed  vessels 
(sealed  glass  tubes),  but  the  pressures  produced  are  not  great, 
and  there  is  little  risk  of  the  tubes  being  burst. 

Acetamide,  CH3CONH2,  is  best  prepared  by  the  third 
method.  It  is  separated  from  unaltered  ammonium  acetate  by 
distillation,  and  is  obtained  as  a  white  solid,  usually  possessing 
a  characteristic  odour  of  mice,  but  apparently  odourless  when 
quite  pure.  It  is  not  markedly  acid  or  basic  in  behaviour, 
the  basic  character  of  the  ammonia  being  removed  by  the 
introduction  of  the  acid  radicle. 

When  boiled  with  much  water  acetamide  is  slowly  converted 
into  ammonium  acetate  : 

CH3CONH2  +  H,O    =    CH3COONH4, 
Acetamide.  Ammonium  acetate. 

and  the  same  change  takes  place  much  more  readily  when  an 
acid  or  alkali  is  present. 

With  an  alkali  ammonia  is  evolved  ;  with  an  acid  the  ammonium  salt 
of  that  acid  is  formed. 


90  GLYCOCOLL  CHAP. 


AMIDO-ACIDS 

The  amido-acids  are  derived  from  acids  such  as  acetic, 
CH3  .  CO0H,  by  introduction  of  an  amido-group,  NH2,  in  place 
of  one  of  the  hydrogens  of  the  alkyl  radicle  (in  this  case 
methyl,  CH3)  ;  thus  amido-acetic  acid  is  NH2CH2  .  CO2H. 

The  amido-acids  are  neutral  to  litmus,  but  chemically  act 
both  as  acids  and  bases.  They  form  salts  with  copper,  silver, 
and  other  metals  on  the  one  hand,  while  on  the  other  they  com- 
bine with  strong  acids  to  form  salts,  such  as  HC1.NH2CH2CO2H, 
in  which  the  amido-acid  plays  the  part  of  a  substituted 
ammonia. 

Many  amido-acids  occur  in  various  animal  tissues,  and  may 
be  prepared  from  them.  The  most  important  and  instructive 
artificial  methods  for  their  preparation  are  the  following  : — 

( i )  By  acting  with  ammonia  on  a  halogen  derivative  of  the 
acid,  e.g.  monochlor-acetic  acid,  CH2C1  .  CO2H,  yields  amido- 
acetic  acid,  NH2CH2  .  CO2H  : 

CH2C1.CO2H  +  2.  NH3  =  NH2CH2CO2H  +  NH4C1. 
Monochlor-acetic  acid.  Amido-acetic  acid. 

In  practice  the  ammonia  is  obtained  from  solid  ammonium 
carbonate,  which  is  heated  with  the  monochlor-acetic  acid. 

Monochlor-acetic  acid  is  formed  when  chlorine  acts  upon 
acetic  acid  : 

CH3C02H  +  Cl,  =  CH,C1  .  CO2H  +  HC1. 

(2)  The  second  method,  somewhat  more  complicated,  starts  from  the 
aldehydes.  These  are  able  to  combine  with  ammonium  cyanide  to  form 
compounds,  such  as  CH3  .  CH(NH2)(CN)  : 

XTtT 

CH3.  CHO  +  NH4CN  =  CH3.  CH<££2+H2O. 

These  when  treated  with  dilute  acids  (see  p.  69)  yield  amido-acids  by  con- 
version of  the  CN  group  into  carbo.xyl,  CO2H. 

Amido- Acetic  Acid,  NH2  .  CH2CO2H  (Glycocoll),  can 
be  extracted  from  glue  (therefore  from  bones)  by  treatment  with 
sulphuric  acid  ;  it  is  best  prepared  synthetically  from  mono- 
chlor-acetic acid  by  the  action  of  ammonia.  It  forms  a  dark- 
blue  copper  salt  (NH2CH2CO2)2Cu,  and  also  a  chloride, 


LEUCIN  91 


HC1 .  NH.,CH2CO2H.      Glycocoll  itself  is  a  white  crystalline 
solid,  having  a  sweetish  taste,  and  readily  soluble  in  water. 

Of  the  more  complicated  amido-acids  we  may  mention 
Leucin,  C4H0  .  CHNH2  .  CO2H,  therefore  amido-caproic 
acid,  which  is  one  of  the  most  important  products  of  the 
decomposition  of  albumen,  either  by  putrefaction  or  by  boiling 
with  acids  or  alkalies  ;  it  is  also  present  ready-formed  in 
various  glands  of  the  body  as  the  pancreas,  spleen,  etc. 


QUESTIONS  ON  CHAPTER  XII 

i.  What  substances  are  formed  by  the  action  of  ammonia  upon  (a) 
monochlor-acetic  acid,  (/>)  methyl  chloride,  (c)  acetyl  chloride?  Give 
equations. 

•2.  What  is  the  action  of  dilute  hydrochloric  acid  upon  (a)  acetamide, 
(b)  glycocoll? 

3.  Describe  the  preparation  of  acetamide  and  of  glycocoll  from  acetic 
acid. 


CHAPTER    XIII 

ALKYL  COMPOUNDS  OF   PHOSPHORUS,  ARSENIC, 
SILICON,    AND    THE    METALS 

COMPOUNDS   OF    PHOSPHORUS 

Phosphines. — Phosphine,  PH3,  is  much  less  basic  in  char- 
acter than  ammonia,  but  is  yet  capable  of  combining  with 
hydrogen  iodide  to  form  the  compound  phosphonium  iodide, 
PH4L  The  organic  phosphines,  obtained  by  substituting  the 
hydrogen  in  PH,{  by  alkyl  groups,  are  stronger  bases  in  pro- 
portion to  the  number  of  alkyl  groups  introduced. 

By  the  action  of  alkyl  iodides  on  PH3  only  tertiary  phos- 
phines, PR3,  and  phosphonium  compounds,  PR4I,  are  obtained. 
The  primary  and  secondary  bases  can,  however,  be  prepared 
by  employing,  instead  of  PH.,,  a  mixture  of  PH4I  with  oxide  of 
zinc.  The  separation  of  these  bodies  is  not  then  difficult,  and 
depends  on  the  gradual  increase  in  their  basic  character 
from  primary  phosphine  to  phosphonium  compounds  : 

Tetra-methyl  phosphonium  iodide,  P(CH3)4I,  is  not  decom- 
posed by  KOH. 

Tri-methyl  phosphonium  iodide,  P(CH3)3.HI,  is  decom- 
posed by  KOH. 

Dimethyl  phosphonium  iodide,  HP(CH3)., .  HI,  is  not  decom- 
posed by  water. 

Methyl  phosphonium  iodide,  H2PCHg  .  HI,  is  decomposed 
by  water. 

The  phosphines  are  gases  or  volatile  liquids,  very  inflam- 


CHAP,  xin  THE  PHOSPHINES  93 

mable,  and  possessed  of  very  strong  unpleasant  odours.  Char- 
acteristic of  the  tertiary  phosphines  is  the  readiness  with  which 
they  combine  with  O,  S,  C12,  etc.,  to  form  compounds  such  as 
P(C2H5)3O,  triethyl-phosphine  oxide,  in  which  the  radicle 
P(C2H5)3  plays  the  part  of  a  divalent  metal. 

Methyl-phosphine,  PH2(CH3),  is  obtained  along  with 
diethyl-phosphine,  PH(CH3)2,  by  heating  a  mixture  of 
phosphonium  iodide  with  methyl  iodide  and  zinc  oxide  in 
sealed  tubes  to  a  temperature  of  150°  C.  : 

2PH4I  +  2CH3I  +  ZnO  =  2PH2(CH3)  .  HI  +  ZnI2  +  H2O, 
Phosphonium  Methyl-phosphonium 

iodide.  iodide. 

PH4I  +  2CH3I  +  ZnO  =  PH(CH3)2  .  H I  +  ZnI2  +  H2O. 
Dimethyl-phosphonium  iodide. 

On  heating  the  resulting  product  with  water,  the  methyl- 
phosphine,  PH2CH3,  is  liberated,  while  the  dimethyl-phosphine, 
PH(CH3)2,  remains  combined  with  the  hydriodic  acid.  On 
subsequently  boiling  with  sodium  hydrate,  the  secondary 
phosphine  is  in  turn  set  free. 

Trimethyl-phosphine,  P(CH3)3,  is  prepared  by  heating 
phosphonium  iodide  with  methyl  iodide  without  the  addition 
of  zinc  oxide  : 

PH4I  +  3CH3I  =  P(CH3)3  .  HI  +  3HI. 

Trimethyl-phosphonium  iodide. 

The  phosphine  is  obtained  when  the  product  is  decomposed 
by  boiling  with  potash  or  soda. 

All  three  of  these  methyl-phosphines  are  very  inflammable, 
and  exhibit  intolerable  odours  ;  they  readily  combine  with 
chlorine,  bromine,  oxygen,  or  sulphur  to  form  compounds 
such  as  P(CH3)30  or  PH(CH3)2C12. 


COMPOUNDS   OF    ARSENIC 

The  Arsines  are  connected  with  AsH3  as  the  amines  with 
NH3.  No  primary  or  secondary  arsines  (such  as  AsH9CH3) 
are  known,  but  tertiary  compounds,  As(CH3)3,  etc.,  have  been 


94  CACODYL  COMPOUNDS  CHAP. 

prepared.  These,  like  the  parent  substance  AsH3,  are  incapable 
of  forming  salts. 

The  most  important  organic  compounds  of  arsenic  form  a 
series  in  which  the  radicle  As(CH3)2  corresponds  to  an  atom 
of  a  monovalent  metal,  and  it  has  been  found  convenient  to 
give  a  special  name  —  cacodyl  —  to  this  radicle. 

Cacodyl  Oxide,  {As(CH3)2}2O  or  Cdl9O,  can  be  obtained 
by  distilling  As2O3  with  potassium  acetate  : 

4CH3  .  C02K  +  As203  =  *>°  +  2K2C°*  +  2CO2> 


Potassium  acetate.  Cacodyl  oxide. 

and  from  this  oxide,  by  the  action  of  acids,  various  salts  can  be 
made,  amongst  them  cacodyl  chloride,  As(CH3)2Cl,  which 
when  reduced  with  zinc  furnishes  free  cacodyl,  As0(CH3)4. 
All  of  these  compounds  are  liquids  of  disgusting  odour  and 
intensely  poisonous  properties.  They  are  also  very  inflammable, 
and  their  investigation,  which  was  carried  out  by  Bunsen,  was 
a  matter  of  great  danger  and  difficulty, 

Of  the  organic  compounds  of  arsenic,  other  than  the  cacodyl 
derivatives,  we  will  mention  only  one. 

Arsenic  Trimethyl,  As(CHH)s,  which  is  obtained  by  the 
action  of  methyl  iodide  upon  an  alloy  of  arsenic  and  sodium. 
It  is  a  colourless  volatile  liquid  of  unpleasant  smell,  readily 
combining  with  one  atom  of  oxygen  or  two  of  chlorine  to  form 
compounds  in  which  the  arsenic  is  pentavalent,  e.g.  As(CH3)3O, 
As(CH3)3Cl2.  It  is  not  basic  in  character,  and  has  no 
tendency  to  combine  with  acids  to  form  salts  in  the  same 
way  as  N(CH3)3  and  P(CH3)3. 

COMPOUNDS   OF   SILICON 

The  organic  derivatives  of  the  tetravalent  element  silicon 
may  be  put  side  by  side  with  other  organic  compounds  in 
which  the  place  of  the  silicon  is  taken  by  carbon,  itself  a 
tetravalent  element  ;  thus  — 

Silicon  Tetramethyl,  Si(CH3)4,  may  be  compared  with 
the  pentane  C(CH3)4  ;  it  is  obtained  by  treating  silicon 
tetrachloride  with  zinc  methyl  (see  p.  95)  : 

SiCl4  +  2Zn(CH3)2  =  Si(CH3)4  +  2ZnCl2, 


ZINC  METHYL  95 


and  is  a  volatile  liquid  unaltered  by  water.  The  analogy  with 
the  pentane,  C(CH3)4,  is  not  merely  one  of  formulae,  but  is  also 
seen  to  some  extent  in  the  chemical  behaviour  of  the  two  com- 
pounds. This  is  not  surprising  in  view  of  the  fact  that  both 
are  of  similar  type,  and  each  contains  four  methyl  groups  ;  but 
that  there  exists  no  complete  analogy  between  the  silicon 
derivatives  and  those  of  carbon  is  evident  from  the  great 
differences  between  the  simple  corresponding  derivatives  of  the 
two  elements;  thus  silico-chloroform,  SiHCl3,  is  a  liquid  fuming 
in  the  air  and  decomposed  by  water,  therefore  quite  unlike 
chloroform  itself,  CHC13. 

COMPOUNDS    OF    THE    METALS    WITH    ALKYL    RADICLES 

Many  of  the  metals  form  alkyl  compounds,  usually  volatile 
liquids  which  oxidise  rapidly  or  even  ignite  spontaneously  in 
the  air ;  they  are  obtained  by  the  action  of  alkyl  iodides  upon 
the  metals,  or  upon  their  alloys  with  zinc  or  sodium. 

A  second  method  is  to  act  with  zinc  methyl  (or  zinc  ethyl, 
etc.)  upon  the  chloride  of  the  metal  which  is  to  be  converted 
into  an  alkyl  derivative. 

Zinc  Methyl,  Zn(CH3)2,  is  obtained  by  the  action  of 
methyl  iodide  upon  zinc  and  subsequent  distillation.  In  the 
first  place,  direct  combination  of  the  zinc  and  methyl  iodide 
occurs  : 

Zn     +     CH3I     =     Zn<CjH3- 

Methyl  iodide.      Zinc  methyl-iodide. 
The  compound  thus  formed  is  decomposed  by  further  heating  : 

/-•TT 

2Zn<    j  3    =    Zn(CH3)2  +  ZnI2. 
Zinc  methyl-iodide.       Zinc  methyl. 

The  first  reaction  takes  place  more  readily  when  the  zinc- 
copper  couple  of  Gladstone  and  Tribe  is  used  instead  of  zinc 
filings.  This  couple  is  merely  an  intimate  mixture  of  finely 
divided  copper  and  zinc,  and  can  be  most  readily  prepared  by 
mixing  zinc  filings  with  one-ninth  of  their  weight  of  copper-dust, 
obtained  by  reducing  powdered  copper  oxide  in  a  current  of 


96 


ZINC  ETHYL 


CHAP. 


hydrogen.      The  couple  only  requires  to  be  heated  for  a  few 
minutes  in  a  flask  to  make  it  ready  for  use. 

EXPT.  18.  Mix  90  grams  zinc  filings  with  10  grams  of  reduced  copper. 
Place  the  mixture  in  a  flask  fitted  with  cork  and  capillary  tube,  and  heat 
for  a  few  minutes  over  the  bare  flame  of  a  Bunsen  burner.  When  cool, 


FIG.  29.  -  Preparation  of  Zinc  Ethyl. 

add  50  grams  methyl  iodide,  and  fit  the  flask  with  an  inverted  condenser 
and  a  tube  for  introducing  coal-gas  (see  fig.  29).  Heat  on  the  water  bath 
for  ten  hours  ;  then  arrange  the  condenser  for  distillation  and  distil  off 
the  zinc  methyl  in  a  slow  current  of  coal-gas. 

Zinc  Ethyl,  Zn(C0H,).,,  is  similarly  prepared.  Both  are 
important  laboratory  reagents  for  the  purpose  of  introducing 
methyl  or  ethyl  groups  in  the  place  of  chlorine  or  other 


XIII  LEAD  TETRA-ETHYL  97 


element,  e.g.  a  ketone  can  be  made  by  the  action  of  zinc  ethyl 
on  acetyl  chloride  : 

2CH3  .  CO  .  Cl  +  Zn(C2H5)2  =  2CH3  .  CO  .  C2H5  +  ZnCl2. 
Acetyl  chloride.  Methyl-ethyl  ketone. 

Zinc  methyl  and  ethyl  fume  in  the  air  and  very  readily  take 
fire,  often  spontaneously.      They  are  decomposed  by  water  : 


Zn(CH3)2  +  2H20  =  Zn(OH)2 

Zinc  methyl.  Methane. 


and  by  the  halogens  : 


Zinc  ethyl.  Ethyl  iodide. 

Mercury  Methyl,  Hg(CH3)2,  and  Mercury  Ethyl, 
Hg(C2H5)2,  are  colourless  liquids,  whose  vapours  have  only 
feeble  odour,  but  are  very  poisonous  ;  they  are  prepared  from 
sodium  amalgam  by  the  action  of  methyl  or  ethyl  iodide  : 

NaHg     +     2CH3I  2NaI   +   Hg(CH3)2. 

Methyl  iodide.  Mercury  methyl. 

They  are  more  stable  than  the  zinc  compounds,  and  neither 
take  fire  in  the  air  nor  are  decomposed  by  water.  Their 
general  chemical  behaviour  is  otherwise  similar  to  that  of  their 
zinc  analogues. 

Alkyl  Compounds  of  other  Metals.  —  Many  other 
metals  also  form  similar  compounds,  the  most  important  cases 
being  perhaps  those  of  lead  and  tin. 

By  acting  on  lead  chloride,  PbCl2,  with  zinc  ethyl  the  sub- 
stance lead  tetra-ethyl,  Pb(C2H5)4,  is  obtained  : 

2PbCL>  +  2Zn(C,H5)2  =  Pb(C2H5)4  +  Pb  +  2ZnQ2, 

a  fact  which  proves  that  lead  is  really  a  tetravalent  element, 
and  is  thus  in  complete  agreement  with  the  recent  discovery 
of  the  existence  of  a  lead  tetrachloride,  PbCl4.  Lead  tetra- 
ethyl  is  an  oily  liquid  which  takes  fire  when  heated  in  contact 
with  air. 

In  the  same  way,  by  acting  on  stannous  chloride,  SnCl2,  with 

H 


98  TIN  ETHYL  CHAP,  xm 

zinc  ethyl,  we  obtain  tin  tetra-ethyl,  Sn(C9H5)4,  in  which  the 
maximum  valency  of  the  metal  is  exerted  : 

2SnCl2+2Zn(C2H5)2  -   Sn(C2H5)4  +   Sn-f  2ZnQ2; 
Zinc  ethyl.  Tin  tetra-ethyl. 

but  tin  di-ethyl,  Sn(C2H5)2,  can  be  got  by  treating  an  alloy 
of  tin  and  sodium  with  ethyl  iodide  : 

SnNa  +   2C2H5I   =  Sn(C2H5)2  +   2NaI. 
Ethyl  iodide.      Tin  di-ethyl. 

Sn(C2H5)4  is  a  liquid  which  can  be  distilled  without  decom- 
position, whereas  Sn(C2H5)2  decomposes  into  the  tetra-ethyl 
compound  and  metallic  tin. 


QUESTIONS  ON  CHAPTER  XIII 

i.  Give  the  preparation  of  (a)  phosphorium  iodide,  (b]  tetra-methyl 
phosphonium  iodide.  What  is  the  action  of  water  and  of  potassium 
hydrate  solution  upon  these  two  compounds  ? 

•2.  How  is  free  cacodyl  obtained  ?  Give  the  formulae  of  cacodyl  oxide 
and  cacodyl  chloride. 

3.  Give  the  preparation  of  zinc  ethyl.     What  is  the  action  upon  it  of 
(a)  water,  (b]  chlorine,  (c]  acetyl  chloride  ? 

4.  What  reasons   have  we  for  considering    lead  to  be  a  tetra-valent 
metal  ? 


CHAPTER    XIV 

GLYCOL  AND   ITS   DERIVATIVES.       SUCCINIC, 
MALIC,   AND  TARTARIC  ACIDS 

Glycol,  C2H4(OH)2,  is  a  substance  containing  two 
hydroxyls  combined  with  the  divalent  radicle,  C2H4,  ethylene. 
Each  of  these  hydroxyls  behaves  similarly  to  the  hydroxyl  in 
an  alcohol,  so  that  glycol  may  be  termed  a  dihydric  alcohol. 

It  is  obtained  from  ethylene  bromide,  C0H4Br2,  by  replace- 
ment of  the  bromine  : 


C,H4Br,    +    2HOH  =  C2H4(OH)2 

Ethylene  bromide.  Glycol. 

just  as  the  ethyl  alcohol  can  be  got  from  ethyl  bromide  : 
C2H5Br  +  HOH  =  C2H5OH  +  HBr. 

It  is  necessary  when  preparing  glycol  from  ethylene  bromide 
in  this  way  to  heat  with  a  large  quantity  of  water  to  temper- 
atures of  150°  C.   or  thereabouts;    the  reaction   takes   place 
more  readily  when  sodium  carbonate  is  added  to  the  water. 
This   method   of  preparation    indicates    the    constitutional 

CH2OH 

formula    |  for  glycol,  according  to  which  it  may  be  re- 

CH2OH 

garded  as  a  dihydric  primary  alcohol,  and  this  view  is  strength- 
ened by  consideration  of  the  substance's  general  chemical 
behaviour. 


ioo  GLYCOL  A  DIHYDRIC  ALCOHOL  CHAP. 

As  a  dihydric  alcohol  glycol  reacts  with  sodium  or  potas- 
sium to  form  glycolates  analogous  to  the  alcoholates  (p.  44)  : 

O  FT 
C2H4(OH)2  +  Na  =  C2H4<QNa  +  H' 

and 

C2H4(OH)2  +  2Na  =  C2H4(ONa)2  +  H2  ; 

and  ethereal  salts  of  glycol  can  be  obtained  by  the  action  on 
it  of  acids  : 

C2H4(OH)2  +  2CH3CO2H  =  C2H4(OC02CH3)2  +  2H2O  ; 
Glycol.  Acetic  acid.  Ethylene  acetate. 

just  as  ethyl  acetate  is  got  from  ethyl  alcohol  and  acetic  acid, 
so  here  ethylene  acetate  is  obtained. 

As  a  dihydric  primary  alcohol  glycol  furnishes,  when  treated 
with  oxidising  agents,  bodies  in  which  the  groups  CH2OH  are 
successively  oxidised  to  aldehyde  groups  CHO,  and  finally  to 
carboxyl  groups  CO0H.  The  substances  thus  obtained  are 
presently  to  be  considered. 

Glycol  is  a  thick  colourless  liquid  with  a  sweetish  taste. 

The  isomeric  glycol,  ethylidene  glycol,  CH3 .  CH(OH)2,  does  not  seem 
able  to  exist  unless  in  dilute  solution  ;  instead  of  this  we  obtain  aldehyde 
CH3 .  CHO  when  the  ethylidene  glycol  might  be  expected,  e.g.  in  action 
of  water  on  CH3  .  CHC12. 

Glyoxal,  (CHO).,,  is  the  di-aldehyde  of  glycol,  and  is 
formed  along  with  other  substances  in  the  oxidation  of  glycol  : 

CH2OH  CHO 

I  +0=    i         +H20. 

CH2OH  CHO 

Glycol.  Glyoxal. 

Like  other  aldehydes,  it  readily  reduces  Fehling's  solution  or 
ammoniacal  silver  solution  (see  p.  62). 

Glycolic  Acid,  CH2(OH)  .  CO2H,  is  also  formed  in  the 
oxidation  of  glycol  : 

CH.,OH  CH2OH 

I  +02=*   I  +H,0, 

CH2OH  CO,H 

Glycol.  Glycolic  acid. 


xiv  OXALIC  ACID 


but  is  better  prepared  from  mono-chloracetic  acid  by  boiling 
with  water,  to  which  calcium  carbonate  in  fine  powder  has 
been  added  (to  combine  with  the  HC1)  : 

/~*TT     /"*1          /"*  /~\     TT  T  T     /"\      J     /^T-fr  ±  /  f*\  tY  \  /      /"•  f~\      /T     Jt    -i"^JT /^*1 

t/HgCl .  CUgH     +     H2O  -~c  Lllfl-itry.  ,CO2H,4-,HC1. 

Monochlor-acetic  acid.  v  J-     ,      o  Glvcpjip  acid.,o  »     .,  ,    - 

Glycolic  acid  forms  white  crystals.'  As  an  acid  it  yields  well- 
defined  salts,  such  as  silver  glycolate,  CH2OH  .  CO2Ag,  while 
as  an  alcohol  it  combines  with  acids  to  produce  ethereal  salts. 
Oxalic  Acid,  (CO2H)2,  is  a  more  completely  oxidised  pro- 
duct of  glycol : 

CH2.OH  CO.H 


209   =     |  +2H20. 

Glycol.  Oxalic  acid. 


CH2  .  OH  CO2H 


It  is  an  important  acid,  the  starting-point  of  a  series  of  organic 
dibasic  acids.  Oxalic  acid  is  found  in  many  plants,  especially 
the  varieties  of  Oxalis,  and  can  be  prepared  artificially  in  several 
ways,  of  which  three  further  ones  (in  addition  to  the  oxidation 
of  glycol)  may  be  mentioned  : 

(1)  Carbon  dioxide  when  passed  over  heated  metallic  sodium 
combines  with  it  to  form  sodium  oxalate  : 

2CO2  +  2Na      =      C204Na2. 

Sodium  oxalate. 

(2)  Sodium  formate  when  strongly  heated  evolves  hydrogen 
and  yields  sodium  oxalate  : 

2H.C02Na  =  H2      +      C204Na2 
Sodium  formate.  Sodium  oxalate. 

(3)  An  important  practical  method  for  the  manufacture  of 
oxalic   acid   is  the   action   of  caustic  alkalies  upon  cellulose. 
Sawdust  (the  form  of  cellulose  generally  used)  is  mixed  into  a 
paste  with  a  strong  solution  of  potash,  and  then  heated  on  iron 
plates.     The  product  is  extracted  with  water,  and  the  oxalic 
acid  separated  by  precipitation  as  calcium  oxalate. 

Oxalic  acid  forms  crystals  which  contain  two  molecules  of 


SUCCINIC  ACID 


water  of  crystallisation.     When  heated  the  crystals  lose  water, 
and  then  decompose  into  formic  acid  and  carbon  dioxide  : 


?,,  =          +      .2. 

Oxalic*  aei(5/  1  Formic  acid. 


Oxalic  acid  wlier.  heated  with  strung  sulphuric  acid  does  not 
blacken^  but  is  'decomposed'  A>'tb  evolution  of  the  two  oxides 
of  carbon  in  equal  volumes  : 

C2O4H2=CO  +  C02  +  H20. 

Oxalic  acid  is  a  stronger  acid  than  acetic,  and  being  a  dibasic 
acid  forms  two  series  of  stable  salts. 

Potassium  Oxalate,  C0O4K2,  is  used  in  preparing  the 
"  ferrous  oxalate  developer,"  largely  employed  in  photography. 

Potassium  Hydrogen  Oxalate,  C9O4KH,  along  with 
free  oxalic  acid,  composes  the  "salts  of  lemon"  used  for  re- 
moving ink-stains  from  cloth. 

Ammonium  Oxalate,  C2O4(NH4)0,  is  used  as  a  reagent 
in  the  laboratory. 

SUCCINIC,    MALIC,    AND   TARTARIC   ACIDS 

Succinic  Acid,  C4H6O4,  was  first  obtained  by  distillation 
of  amber,  and  this  is  still  the  way  prescribed  for  its  preparation 
in  the  British  Pharmacopoeia.  It  is  also  present  in  some  other 
resins  and  in  lignite.  The  artificial  methods  for  making  the 
acid  and  its  reactions  are  best  represented  by  the  constitutional 
formula  given  below  ;  the  chief  of  these  methods  are  : 

(1)  Ethylene  cyanide  (from  ethylene  bromide  and  AgCN), 
when  boiled  with  dilute  acids  or  alkalies,  yields  succinic  acid  : 

CH2  .  CN  CH2  .  CO2H 

I  +  4H20    =    I  +2NH3. 

CH2.CN  CH2.CO2H 

Ethylene  cyanide.  Succinic  acid. 

(2)  Succinic  acid  is  also  obtained  by  the  reduction  of  malic 
acid,  which  can  itself  be  similarly  obtained  from  tartaric  acid  : 

C4H606  O  C4H605. 

Tartaric  acid.  Malic  acid. 


xiv  MALIC  ACID  103 

C4HC05  O  C4H604. 

Malic  acid.  Succinic  acid. 

The  reduction  can  be  effected  by  heating  with  hydriodic  acid  in  sealed 
tubes. 

Succinic  acid  forms  colourless  crystals,  soluble  in  water, 
and  possessing  an  unpleasant  taste. 

Malic  Acid,  C4H6O5,  occurs  in  the  juice  of  apples  and  of 
many  other  fruits.  Its  close  relation  to  succinic  acid  is  indi- 
cated by  the  reaction,  above  referred  to,  by  which  that  acid  is 
obtained  by  the  reduction  of  malic  acid,  and  the  exact  char- 
acter of  the  relation  is  made  clear  by  the  following  method  of 
preparation  : — 

(1)  Malic  acid  is  produced  when  monobrom-succinic  acid 
is  treated  with  silver  oxide  and  water  : 

CHBr  .  CO.,H  CH(OH)  .  CO2H 

I  +  AgOH  =    |  +AgBr. 

CH2  .  C02H  CH2  .  CO2H 

Monobrom-succinic  Malic  acid, 

acid. 

Malic  acid  is  therefore  monohydroxy-succinic  acid. 

(2)  Malic  acid  is  formed  by  the  partial  reduction  of  tartaric 
acid  : 

CeH406    ..    Q    _    C(5H405. 

Tartaric  acid.  Malic  acid. 

Malic  acid  forms  deliquescent  needles.  It  is  a  somewhat 
stronger  acid  than  succinic,  and  forms  several  well-crystallised 
salts.  Very  important  is  the  existence  of  three  isomeric  forms 
of  malic  acid  which  differ  chiefly  in  their  action  upon  polarised 
light.  One  form,  the  ordinary  one  obtained  from  berries, 
rotates  the  plane  of  polarisation  to  the  left ;  a  second  form, 
prepared  from  dextro-tartaric  acid,  rotates  the  plane  of  polar- 
isation to  the  right  ;  while  the  third  form,  obtained  synthetic- 
ally, is  inactive.  The  fuller  consideration  of  this  case  of 
isomerism  is  deferred  until  Part  II.  of  this  book. 

Tartaric  Acid,  C4H6OC,  is  present  in  the  juice  of  many 
fruits,  especially  in  that  of  grapes  ;  practically  the  only  source 
of  the  acid  is  the . "  argol,"  an  impure  potassium  tartrate,  de- 


io4  TARTARIC  ACID  CHAP. 

posited  during  the  fermentation  of  grape-juice.  The  constitu- 
tional formula  of  the  acid  is  evident  from  its  relation  to  malic 
and  succinic  acids  (into  which  it  is  in  turn  converted  by  re- 
duction), and  from  the  following  synthetical  methods  of  pre- 
paration : — 

(i)  Dibrom-succinic  acid  when  boiled  with  water  and  silver 
oxide  yields  tartaric  acid  : 

CHBr .  CO2H  CH(OH)CO2H 

1  +2AgOH=    |  +2AgBr; 

CHBr  .  CO2H  CH(OH)CO2H 

Dibrom-succinic  Tartaric  acid, 

acid. 

tartaric  acid  is  accordingly  dihydroxy-succinic  acid. 

Tartaric  acid  furnishes  another  instance  of  the  existence  of 
isomers  inexplicable  by  the  theory  hitherto  alone  employed  for 
the  explanation  of  cases  of  isomerism.  The  isomers  again 
differ,  just  as  was  the  case  with  the  malic  acids,  chiefly  in  their 
action  upon  polarised  light.  Tartaric  acid  furnishes  four  such 
isomers,  of  which  one  is  dextro-rotatory  (rotates  the  plane  of 
polarisation  to  the  right),  another  is  laevo-rotatory,  while  the 
other  two  are  inactive.  We  shall  here  consider  only  the  com- 
mon variety,  dextro-tartaric  acid,  leaving  the  others  to  be  dis- 
cussed in  Part  II. 

Dextro-tartaric  acid  is  the  tartaric  acid  of  the  shops.  It  is 
prepared  from  argol  by  conversion  into  calcium  tartrate  (treat- 
ment with  milk  of  lime),  and  subsequent  liberation  of  the  free 
acid  by  addition  of  sulphuric  acid.  It  is  purified  by  recrystal- 
lisation,  and  forms  large  prismatic  crystals  which  are  readily 
soluble  in  water.  The  solution  rotates  the  plane  of  polarisa- 
tion of  light  to  the  right.  It  is  a  dibasic  acid,  and  the  follow- 
ing salts  formed  by  it  are  of  importance  : — 

Potassium  Hydrogen  Tartrate,  C4O6H5K,  is  the 
"cream  of  tartar"  of  the  druggist,  and  is  obtained  by  purify- 
ing the  "argol"  deposited  in  the  fermentation  of  grape-juice. 
It  is  only  slightly  soluble  in  water,  and  hence  sodium  hydrogen 
tartrate  will  precipitate  it  from  solutions  of  potassium  salts, 
unless  very  dilute  ;  this  reaction  is  sometimes  used  as  a  test 
for  the  presence  of  potassium  in  place  of  the  more  expensive 
method  by  means  of  platinic  chloride. 


xiv  THE  TARTRATES  105 


Potassium  Sodium  Tartrate,  C4O6H4KNa,  is  known 
as  "  Rochelle  salt,"  and  is  prepared  by  mixing  solutions  of 
sodium  hydrate  and  cream  of  tartar. 

Tartar  Emetic  is  the  name  of  a  substance  which  is  ob- 
tained by  boiling  cream  of  tartar  and  oxide  of  antimony  with 
water.  Its  constitution  is  generally  supposed  to  be  repre- 
sented by  the  formula  C4O6H4(SbO)K,  according  to  which 
one  hydrogen  atom  of  the  tartaric  acid  is  replaced  by  the 
monovalent  group  (Sb'"O),  antimonyl.  Tartar  emetic  is  then 
to  be  termed  potassium  antimonyl  tartrate. 

The  same  group,  SbO,  exists  in  the  compound  which  is  obtained  as  a 
white  precipitate  when  water  is  added  to  a  solution  of  antimony  chloride. 
This  precipitate  has  the  composition  SbOCl,  and  is  produced  according  to 
the  equation 

SbCl3  +  H20  =  SbOCl  +  2HC1. 


QUESTIONS  ON  CHAPTER  XIV 

1.  By  what  reactions  would  you  proceed  to  prepare  glycol  from  ethyl 
alcohol  ? 

2.  Show  by  its  reactions  that  glycol  behaves  as   a  dihydric   primary 
alcohol. 

3.  Give  two  ways  by  which  oxalic  acid  can  be  synthesised  from  its 
elements.      Describe  the  commercial  process  for  the  manufacture  ef  the 
acid. 

4.  What  is  the  relation  between  succinic,  malic,  and  tartaric  acids? 
How  can  you  pass  from  each  of  them  to  the  others  ? 

5.  Write  down  the  formulae  of  (a)  salts  of  lemon,  (b]  tartar  emetic,  (c] 
cream  of  tartar,  (d)  succinic  acid. 


CHAPTER    XV 
LACTIC    AND    CITRIC    ACIDS 

Lactic  Acid  is  a  substance  present  in  sour  milk  which,  when 
isolated  and  examined  as  to  its  chemical  relationship,  is  found 
to  be  predominantly  an  acid,  but  also  to  possess  some  of  the 
properties  of  alcohols.  Its  empirical  formula  is  CH^O  as 
determined  by  analysis,  and  as  the  acid  cannot  be  vaporised 
without  decomposition,  we  are  unable  to  ascertain  its  mole- 
cular weight  by  a  vapour  density  determination.  It  has 
recently  become  possible  to  employ  other  means  for  finding 
the  molecular  weight  of  the  acid  itself,  but  a  little  study  of  the 
compounds  of  lactic  acid  enables  us  to  discover  its  molecular, 
and  then  its  constitutional  formula. 

Lactic  acid  forms  only  one  sodium  salt,  sodium  lactate, 
whose  analysis  indicates  the  formula  C3H5NaO.;,  and  therefore 
the  molecular  formula  C3H6O3  for  the  acid  (this  agrees  with 
the  vapour  density  of  ethyl  lactate  C3H5OS .  C2H5).  Lactic 
acid  is  therefore  a  monobasic-acid,  and  contains  one  carboxyl 
group,  CO2H.  But  in  this  sodium  salt  there  is  yet  left  a 
hydrogen  atom  which  can  with  some  little  difficulty  be  replaced 
by  sodium,  and  behaves  like  the  hydrogen  atom  of  an  alcoholic 
hydroxyl.  Lactic  acid  is  therefore  seen  to  contain  the  group 
OH  also. 

Lactic  acid,  CgH^O.j,  may  therefore  be  written  C.2H4(OH) 
(CO2H),  and  the  only  question  left  to  solve  is  whether  the  OH 
and  the  CO.,H  are  connected  to  the  same  or  to  different 
carbon  atoms,  whether  it  is 

CH2(OH)  CH3 

(a)    |  or  (b)     | 

CH2.C02H  CH<°02H 


LACTIC  ACID  107 


Now  lactic  acid  can  be  got  from  aldehyde,  CH3  .  CHO,  by 
adding  to  it  HCN,  and  boiling  the  product  with  hydrochloric 
acid  (see  pp.  64  and  69)  : 

CH3  .  CHO  — >  CH3  .  CH<££  — ->  CH3 .  CH<^R  . 

Aldehyde.  Lactic  acid. 

and  we  are  thus  led  to  assign  to  lactic  acid  the  formula  ($)  of 
the  two  given  above. 

The  lactic  acid  in  sour  milk  is  produced  from  the  lactose  or 
milk  -  sugar  present  in  milk  by  the  action  of  a  particular 
ferment.  Cane-sugar,  starch,  and  other  carbohydrates  also 
yield  lactic  acid  under  the  influence  of  the  same  ferment : 

C12H22°11     +     H2°     =     4C8H608. 
Milk  or  cane  sugar.  Lactic  acid. 

In  preparing  lactic  acid  the  following  is  a  good  method  of 
procedure : 

One  kilogram  of  cane-sugar  is  dissolved  along  with  about  5  grams  of 
tartaric  acid  in  3^  litres  of  water  ;  after  a  few  days  some  rotten  cheese 
(30  grams)  is  rubbed  into  a  paste  with  sour  milk  (i^  litres),  and  added 
to  the  solution  with  400  grams  of  zinc  oxide.  The  whole  is  left  to 
ferment  in  a  warm  place  for  a  week  or  ten  days.  Then  the  mixture  is 
heated  to  boiling,  filtered,  and  the  filtrate  evaporated.  Crystals  of  zinc 
lactate  separate  out  on  cooling  ;  they  are  collected  and  dissolved  in  water, 
and  the  zinc  removed  by  passing  H^S.  The  zinc  sulphide  is  removed  by 
filtration,  and  the  solution  of  lactic  acid  evaporated  on  the  water  bath. 

Lactic  acid  thus  obtained  is  a  thick  syrupy  liquid.  The  sodium 
salt  has  the  formula  C3H5NaO3,  but  when  this  is  heated  with 
metallic  sodium,  a  second  atom  of  the  metal  is  introduced  in 
place  of  the  alcoholic  hydrogen,  and  a  substance  of  the 
formula  C3H4Na;iO3  is  obtained. 

Lactic  acid  can  also  be  prepared  by  several  synthetical  methods  : 

(1)  From  aldehyde  CH:J .  CHO  (see  above). 

(2)  From  the  bromopropionic  acid,  CHs .  CH2Br  .  CO-jH,  and  potash. 

Great  interest  attaches  to  the  existence  of  an  isomeric  para- 
lactic  acid  which  is  present  in  the  juice  of  meat.  This 


io8  CITRIC  ACID  CHAP. 

behaves  exactly  like  ordinary  lactic  acid  in  nearly  every  other 
respect,  but  differs  from  it  in  being  able  to  rotate  the  plane  of 
polarisation  of  light.  This  is  connected  by  Van't  Hoff,  with 
the  fact  that  one  carbon  atom  in  lactic  acid  is  "  asymmetric," 
that  is,  connected  to  four  dissimilar  radicles.  For  a  fuller 
account  of  this  theory,  see  the  second  part  of  this  book. 

There  is  also  known  another  acid,  hydracrylic,  which  is  isomeric 
with  lactic  acid.  The  formula  (a)  given  above  (p.  106)  is  indicated  for  it 
by  its  formation  from  ethylene  as  indicated  below  : 


CHoOH  CH2OH  CH2OH 

CH2  CHoCl  CH2  .  CN  CH2  .  COoH. 

(+HC10).  (Action  of  KCN).        (Boiling  with  HC1). 

Citric  Acid  is  found  in  lemons,  currants,  cranberries,  and 
many  other  sour  fruits.  It  is  prepared  commercially  from  lemon 
or  lime-juice  by  means  of  the  calcium  salt. 

Its  formula  is  found  by  analysis  to  be  C6H8O7>  and  it 
behaves  as  a  tribasic  acid.  It  contains,  therefore,  three 
carboxyl  groups,  and  forms  salts,  such  as  C6H6(XK3,  and 
ethereal  salts,  such  as  C6H5O7(C2H5)8.  In  these  the  action  of 
acetyl  chloride  proves  the  existence  of  an  hydroxyl  group  (see 
p.  79).  The  acid  therefore  contains  one  OH  and  three  CO2H 
group,  and  its  formula  may  be  written  C3H4(OH)(CO2H)3. 

Citric  acid  crystallises  in  large  prisms.  As  a  tribasic  acid 
it  forms  three  series  of  salts,  the  three  potassium  salts  being 
C6H707K,  CgH6O7K2,  and  C6H5O7K3. 

Calcium  citrate,  (C6H5O7)2Ca3,  is  remarkable  as  being  less 
soluble  in  hot  water  than  in  cold,  a  property  made  use  of  in 
testing  for  citric  acid. 

EXPT.  19.  To  some  solution  of  citric  acid  in  a  test  tube  add  lime 
water  until  the  reaction  is  slightly  alkaline.  No  precipitate  is  formed  in 
the  cold,  but  a  white  precipitate  of  calcium  citrate  appears  on  boiling. 


QUESTIONS  ON  CHAPTER  XV 

i.    How  can  lactic  acid  be  obtained  from  sugar?     Why  is  its  formula 
written  CsHgOg  and  not  CH2O  ? 


CITRIC  ACID  I09 


2.  Mention  some  other  substances  which    have  the  same  percentage 
composition  as  lactic  acid.      How  could  you  distinguish  them  ? 

3.  What  happens  when  (a)  milk  turns  sour,  (b]  butter  turns  rancid,  (c) 
wine  goes  sour  ? 

4.  Write  down  the  formulae  of  (a)  the  three  potassium  citrates,  (d]  zinc 
lactate. 


CHAPTER    XVI 


THE    ALLYL    COMPOUNDS 


THE  allyl  compounds  may  be  regarded  as  being  derived  from 
the  hydrocarbon  propylene,  C3HG,  and  their  starting-point — 
allyl  alcohol — stands  to  propylene  in  the  same  relation  as 
ethyl  alcohol  does  to  ethane. 


FIG.  30. — Preparation  of  Allyl  Alcohol. 

Propylene  has  the  formula  CH2  :  CH  .  CH3,  and  from  this 
three  alcohols  might  be  derived  : 

1.  CH(OH)  :  CH  .  CH3,    a  secondary  alcohol, 

2.  CH2  :  C(OH)  .  CH;i,      a  tertiary 

3.  CH2  :  CH  .  CH,(OH),  a  primary 


CHAP,  xvi  ALLYL  ALCOHOL 


Of  these,  the  third  formula  represents  allyl  alcohol,  which 
in  many  respects  behaves  like  any  other  primary  alcohol, 
but  differs  from  methyl  alcohol  and  its  homologues  in  being 
unsaturated  (see  p.  28).  On  the  one  hand,  as  a  primary 
alcohol,  it  yields  an  aldehyde  and  then  an  acid  when  oxidised, 
while  as  an  unsaturated  compound  it  is  able  to  combine 
directly  with  chlorine  or  bromine. 

Allyl  Alcohol,  C3H5  .OH,  is  obtained  by  distilling  a 
mixture  of  glycerine,  C3H5(OH)3,  with  formic  acid  (oxalic  acid 
may  be  substituted  for  this,  but  as  it  decomposes  under  these 
conditions  into  formic  acid  and  CO2,  the  reaction  is  practically 
the  same).  The  formic  acid  is  oxidised  to  CO2  and  water : 

C3H5(OH)3    +    HCO2H    =    C3H5.  OH  +  CO2+2H2O. 

Glycerine.  Formic  acid.         Allyl  alcohol. 

The  following  is  the  usual  method  for  preparing  allyl 
alcohol : — 

Four  parts  of  glycerine  and  one  of  crystallised  oxalic  acid  are  placed  in 
a  retort  and  gradually  heated.  At  first  much  CO2  is  evolved,  and  dilute 
formic  acid  distils  over.  When  the  temperature  of  the  mixture  reaches 
190°  the  receiver  is  changed,  and  impure  allyl  alcohol  is  obtained  as  the 
distillate.  This  is  purified  by  fractional  distillation,  and  freed  from  water 
by  treatment  with  anhydrous  baryta.  Pure  allyl  alcohol  boils  at  96°. 

Allyl  alcohol  is  a  colourless  liquid  which,  like  all  the  allyl 
compounds,  has  an  irritating,  unpleasant  smell.  As  an  un- 
saturated body  it  combines  directly  with  C10  or  Br9  to  form 
derivatives  of  propyl  alcohol  : 

C3H5  .  OH  +  Br2  =  C3H5Br .  OH. 

Allyl  alcohol.  Dibromo-propyl 

alcohol. 

As  a  primary  alcohol  allyl  alcohol  yields,  when  carefully 
oxidised,  first  an  aldehyde — allyl  aldehyde  or  acrolein — and 
then  an  acid — acrylic  acid  : 

CH2  :  CH  .  CH2OH  +  O  =  CH2  :  CH  .  CHO  +  H2O 
Allyl  alcohol.  Acrolein. 

CH2  :  CH  .  CHO  +  O  =  CH2  :  CH  .  CO2H. 

Acrolein.  Acrylic  acid. 


ALLYL  IODIDE 


Acrolein,  C2H3  .  CHO,  is  also  produced  when  glycerine  or 
fats  (which  are  compounds  of  glycerine)  are  heated  to  decom- 
position. It  is  best  obtained  by  distilling  glycerine  to  which 
twice  its  weight  of  KHSO4  has  been  added  : 

C3H&(OH)3  =  C2H3  .  CHO  +  2H2O. 
Glycerine.  Acrolein. 

Acrolein  is  a  volatile  liquid  with  an  extremely  irritating 
odour.  Its  chemical  behaviour  is  fairly  summed  up  in  the 
statement  that  it  is  an  unsaturated  aldehyde. 

Acrylic  Acid,  C9H0  .  CO9H,  is  best  obtained  from  acrolein 
by  boiling  it  with  water  and  oxide  of  silver  : 

C2H3  .  CHO  +  Ag,0  =  C2H3  ,  C02H  +  2Ag. 
Acrolein.  Acrylic  acid. 

Acrylic  is  a  well-marked  acid.  It  is  of  course  an  un- 
saturated body  and,  as  such,  combines  readily  with  chlorine, 
bromine,  etc.,  to  form  derivatives  of  propionic  acid  : 

C2H3  .  CO2H  +  Br2    =    C2H3Br2  .  CO2H. 

Acrylic  acid.  Dibrom-propionic  acid. 

It  is  a  liquid  similar  to  acetic  acid  in  appearance  and  smell. 

Allyl  alcohol  forms  ethereal  salts  with  acids,  but  of  these 
the  following  are  alone  of  sufficient  importance  to  be  mentioned 
here  :  — 

Allyl  Iodide,  C3H5I,  is  a  colourless  liquid,  which  can  be 
obtained  from  the  alcohol  by  the  action  of  H  I  : 


C3H5.OH  +  HI   -   C3H5I   +   H20, 

Allyl  alcohol.  Allyl  iodide. 

or  more  conveniently  from  glycerine  by  the  action  of  phos- 
phorus and  iodine,  a  reaction  which  may  be  supposed  to  occur 
in  the  two  following  stages  : 

C3H5(OH),  +  PI3     =     C3H5I3     +     H3P03 

Glycerine.  Glyceryl  iodide. 

C3H5I3  C3H5I     +     I2 

Glyceryl  iodide.        Allyl  iodide. 


XVI 


OIL  OF  GARLIC 


The  experimental  details  of  the  second  method  of  prepara- 
tion are  as  follows  : 

A  quantity  of  glycerine  is  freed  from  water  by  heating  in  an  open  dish 
for  at  least  half  an  hour  to  such  a  temperature  that  the  liquid  is  near  its 
boiling  point  and  evolves  abundant  fumes.  The  anhydrous  glycerine  must 
be  placed  in  a  well -stoppered  bottle  while  still  warm. 

A  tubulated  retort  is  fitted  with  a  cork  and  connected  with  an 
apparatus  for  generating  CO2,  so  that  a  slow  current  of  that  gas  can  be 
passed  through  the  retort  during  the  whole  experiment  ;  150  grams  of  the 
anhydrous  glycerine  is  then  placed  in  the  retort,  along  with  100  grams  of 
powdered  iodine  ;  60  grams  of  yellow  phosphorus  is  weighed  out  and  cut 
into  small  pieces,  which  are  taken  up  one  by  one  at  the  end  of  a  knife, 
dried  between  filter-paper,  and  introduced  through  the  tubulus  into  the 
retort.  A  violent  reaction  occurs  as  each  piece  of  phosphorus  is  added, 
and  impure  allyl  iodide  distils  over  ;  it  is  washed  with  a  solution  of  soda, 
separated  by  means  of  a  tap-funnel  from  the  soda,  dried  by  contact  with 
a  few  pieces  of  fused  calcium  chloride,  .and  re-distilled.  Pure  allyl  iodide 
boils  at  101°  C. 


FIG.  31. — Preparation  of  Allyl  Iodide. 


Allyl  Sulphide,  (C3H5).,S,  is  the  chief  constituent  of  oil  of 
garlic,  which  is  obtained  by  distilling  garlic  with  steam,  and 
gives  that  plant  its  characteristic  smell  and  taste.  It  can  be 
prepared  artificially  by  the  action  of  allyl  iodide  upon 
potassium  sulphide  : 

K2S    +    2C3H5I    _    2KI    +    (C3H6)2S. 
Allyl  iodide.  Allyl  sulphide. 

Allyl  Iso-thiocyanate,  C3H5  .  NCS,  is  present  in  oil  of 
i 


ii4  OIL  OF  MUSTARD  CHAP,  xvi 

mustard,  obtained  by  distillation  of  mustard  seeds.  It  can  be 
prepared  artificially  by  the  action  of  allyl  iodide  upon  potassium 
thiocyanate  KCNS  : 

KCNS  +  C3H5I  =  KI  +  C3H5  .  NCS. 
Oil  of  mustard. 

It  is  a  liquid  with  the  strong  penetrating  odour  and  taste  of 
the  natural  "oil  of  mustard." 


QUESTIONS  ON  CHAPTER  XVI 

1.  How  can  allyl  alcohol  he  obtained  from  glycerine?     What  reactions 
stamp  allyl  alcohol  as  an  unsaturated  compound  ? 

2.  By    what    reactions    is    it    possible    to    prepare   acrylic    acid    from 
glycerine  ? 

3.  What  reasons  have  we  for  regarding  allyl  alcohol  as  an  unsaturated 
primary  alcohol  ? 

4.  Give  the  formulae  and  systematic  names  cf  (a)  oil  of  mustard,  (l>] 
oil  of  garlic.      How  can  each  be  prepared  artificially  ? 


CHAPTER    XVII 
GLYCERINE  AND   ITS   COMPOUNDS 

Glycerine  is  contained  in  fats  and  fatty  oils  combined 
with  organic  acids  in  the  form  of  ethereal  salts.  When  these 
compounds  are  heated  with  alkalies  in  the  preparation  of  soap 
the  glycerine  is  set  free,  and  when  the  soap  is  separated  by 
addition  of  salt  from  the  liquor  in  which  the  glycerine  is 
contained,  this  latter  can  be  easily  recovered.  In  many  soaps 
now  manufactured  the  water  and  glycerine  are  not  separated 
from  the  true  soap,  but  the  whole  is  allowed  to  cool,  when  it 
solidifies  to  a  mass  naturally  less  firm  than  a  pure  soap  and 
less  durable,  but  pleasanter  to  use  and  far  more  profitable  to 
manufacture.  Soap  manufacture  is  accordingly  not  a  very 
important  source  of  glycerine  ;  far  more  is  obtained  in  the 
preparation  of  stearic  acid  for  candles.  The  best  process 
conducts  the  saponification  of  the  fat  by  means  of  superheated 
steam  with  the  use  of  a  small  proportion  of  lime.  Stearic 
acid  (mixed  with  other  fatty  acids)  and  glycerine  are 
produced  : 

Fat  +  Water  =  Stearic  Acid  +  Glycerine. 

Glycerine  is  found  by  analysis  to  have  the  formula  C3HgO3. 
It  behaves  as  a  trihydric  alcohol,  and  yields  ethereal  salts 
with  various  acids,  in  which  three  acid  groups  are  introduced 
into  the  glycerine  molecule  ;  this  leads  us  to  write  the  formula 
as  C3H5(OH)3. 

Glycerine  when  perfectly  pure  forms  colourless  crystals 
which  melt  at  17°  G,  about  the  ordinary  temperature  of  a 
room.  It  is,  however,  very  hygroscopic,  and  a  trace  of  water 


n6  GLYCERINE  CHAP. 

is  sufficient  to  convert  it  into  a  syrupy  liquid  ;  this  has  a 
sweet  taste,  and  is  sometimes  added  to  wine  to  give  it  body 
and  sweetness.  It  is  also  used  as  a  cosmetic  and  for  keeping 
leather  articles  soft  and  pliable  ;  it  is  the  starting-point  in  the 
manufacture  of  nitro-glycerine  and  dynamite. 

When  distilled  under  the  ordinary  pressure,  glycerine  is 
largely  decomposed,  acrolein  being  one  of  the  principal 
products  : 

C3H5(OH)3    =    C,H40  +  2H20, 
Glycerine.  Acrolein. 

but  under  diminished  pressure  or  in  a  current  of  superheated 
steam  it  can  be  distilled  without  decomposition. 

Glycerine  can  be  prepared  synthetically  from  allyl  tribromide 
CH2Br.  CHBr.CH2Br,  just  as  glycol  from  CH2Br  .  CH2Br  and  ethyl 
alcohol  from  C2H5Br  ;  its' constitutional  formula  is  CH2(OH)  .  CH(OH) . 
CH2(OH),  and  when  oxidised  it  yields  first  glyceric  and  then  tartronic 
acids  : 

CH2 .  OH  CO2H  CO2H 

I  I 

CH  .  OH          >        CH  .  OH 

I  I 

CH2.  OH  CH2.  OH 

Glyceric  acid. 

The  most  important  compound  of  glycerine  is  the  nitrate, 
generally  known  as  nitro-glycerine;  this  is  obtained  by  the 
action  upon  glycerine  of  a  mixture  of  concentrated  sulphuric 
and  nitric  acids  ;  the  product  is  added  to  water  when  the 
nitro-glycerine  separates  as  an  oil,  which  has  to  be  thoroughly 
washed  before  being  stored  or  worked  up  into  dynamite,  as 
otherwise  the  traces  of  acid  left  in  the  oil  render  it  liable  to 
explode  on  very  slight  provocation. 

Nitro-glycerine  has  the  constitution  C8H&(NO3)H  ;  it  is  the 
nitrate  of  the  tri-valent  radicle  C3H5  (glyceryl),  and  its 
formation  is  represented  by  the  equation  : 

C3H5(OH)3  +  3HN03  =  C3H5(N08)3  +  3H2O. 
Glycerine.  Glyceryl  nitrate 

or  nitro-glycerine. 

The  sulphuric  acid   used   in  its  manufacture  merely  aids   the 


xvii  NITROGLYCERINE  117 

action  of  the  nitric  acid  by  combining  with  the  water 
produced. 

By  boiling  with  water  and  an  alkali,  nitro-glycerine  (like 
other  ethereal  salts)  is  converted  into  the  alcohol  and  acid 
from  which  it  was  formed  : 

C3H5(N03)3  +  3KOH  =  C3H5(OH)3  +  3KNO3. 

Nitro-glycerine.  Glycerine. 

Nitro-glycerine,  like  most  other  similar  compounds  (see  gun- 
cotton,  p.  126),  decomposes  very  readily  when  heated  or 
exposed  to  sudden  shock.  The  substance  contains  more 
oxygen  than  is  required  to  burn  up  the  carbon  and  hydrogen 
contained  in  it : 

2C3H5(N03)3  =  6C02  +  5H20  +  3N2  +  O  ; 

hence  no  oxygen  from  outside  is  required,  and  nitro-glycerine 
can  burn  or  explode  when  cut  off  from  contact  with  air. 
Moreover,  the  oxygen  with  which  the  carbon  and  hydrogen 
combine  is  present  in  the  same  molecule  with  them,  and  in 
consequence  the  change  represented  in  the  above  equation 
takes  place  with  extreme  rapidity  and  suddenness  when  once 
started.  The  heat  produced  in  the  reaction  is  therefore  also 
very  suddenly  developed,  and  the  destructive  power  of  nitro- 
glycerine is  far  in  excess  of  that  of  a  quantity  of  gunpowder, 
which  in  burning  would  give  out  the  same  total  amount  of 
heat. 

Nitro-glycerine  is  a  very  dangerous  substance  to  handle,  as 
even  when  very  carefully  prepared  it  requires  only  a  slight 
shock  to  make  it  explode.  This  disadvantage  is  largely 
removed  in  dynamite,  which  is  a  mixture  of  nitro-glycerine 
with  very  fine  siliceous  earth.  More  recently  this  has  been 
almost  superseded  by  blasting- gelatine,  a  jelly-like  solid 
obtained  by  dissolving  gun-cotton  in  nitro-glycerine,  which  is 
even  safer  to  handle,  and  can,  by  varying  the  proportions,  be 
made  in  different  grades  of  violence  according  to  the  purpose 
intended.  By  addition  of  camphor,  or  other  appropriate 
substance  to  this  mixture,  a  material  is  obtained  of  sufficiently 
moderate  explosive  power  to  be  used  in  ordinary  firearms — 
the  modern  smokeless  powder. 


n8  THE  CHLORHYDRINS  CHAP,  xvn 

Of  some  theoretical  interest  are  the  chlorhydrins, 
compounds  obtained  from  glycerine  by  the  action  of  HC1  or 
of  PC15  ;  in  these  the  hydroxyl  groups  of  the  C.,H5(OH)3  are 
more  or  less  completely  replaced  by  chlorine ;  they  are 
ethereal  salts  of  the  trihydric  alcohol  glycerine  and  hydro- 
chloric acid. 

There  are  two  mono-chlorhydrins,  (a)  CH2(OH) .  CH(OH) .  CH2C1 
and  (/3)  CH2(OH).  CHC1 .  CH2(OH),  of  which  the  first  is  obtained  by 
the  action  of  HC1  on  glycerine. 

Of  the  two  di-chlorhydrins  one  has  the  formula  CH2C1 .  CH(OH) . 
CH.,C1,  and  is  obtained  by  the  action  of  HC1  on  glycerine  ;  the  other  one 
is  CH2C1 .  CHC1 .  CH2(OH),  and  is  the  addition  product  of  allyl  alcohol 
(see  p.  in)  and  Clo. 

Trichlorhydrin,  C3H5C13(CH2C1  .  CHC1 .  CH2C1),  is  the 
final  result  of  the  action  of  HC1  (or  better,  PC15)  upon 
glycerine  ;  it  is  one  of  the  five  possible  isomeric  trichloro- 
propanes,  and  is  a  liquid  with  a  smell  like  chloroform. 

QUESTIONS  ON  CHAPTER  XVII 

1.  What  is  the  chemical  constitution  of  fat?     How  are  the  fats  worked 
up  in  the  manufacture  of  glycerine  ? 

2.  What  happens  to  glycerine  (a)  when   heated  in  the  air,   (l>)  when 
treated  with  a  mixture  of  nitric  and  sulphuric  acids? 

3.  What  chemical    changes  occur  when   nitro-glycerine  (a)  explodes, 
(b)  is  heated  gently  with  dilute  caustic  soda? 

4.  How  is  the  dangerous  violence  of  nitro-glycerine  modified  in  several 
modern  explosives  ? 


CHAPTER    XVIII 
THE  CARBOHYDRATES 

The  Carbohydrates  are  a  class  of  bodies  of  extreme 
importance,  especially  in  plant  life ;  not  only  are  they  the 
chief  constituents  of  all  plants,  but  they  are  also  present  in 
many  animal  tissues. 

All  the  carbohydrates  are  composed  of  the  three  elements, 
carbon,  hydrogen,  and  oxygen,  and  of  these  elements  the  two 
latter  are  present  in  the  proportion  in  which  they  combine  to 
form  water  ;  their  number  is  very  large,  and  their  accurate 
investigation  is  surrounded  with  such  difficulties  that  only 
in  recent  years  has  much  real  knowledge  of  their  chemistry 
been  gained. 

The  chief  difficulty  was  that  no  reagent  was  known  with  which  the 
carbohydrates  would  yield  well-characterised  products  ;  the  compounds 
which  they,  as  aldehyde  and  ketone-alcohols,  form  with  phenyl-hydrazine 
can,  however,  for  the  most  part  be  distinctly  and  easily  recognised,  and  it 
is  by  their  help  that  much  of  our  recent  knowledge  in  this  field  has  been 
won. 

THE  GLUCOSES 

The  first  family  of  the  carbohydrates  to  be  considered  is 
the  Glucoses  ;  these  have  the  empirical  formula  CH2O,  and 
most  of  them  have  the  molecular  formula  C6H12O6,  as  has 
been  proved  by  the  application  of  Raoult's  method  for  the 
determination  of  molecular  weights  (see  p.  16). 

There  are,  however,  bodies  known  of  the  molecular  formulae  C5HioO5 
(arabinose)  and  C7H14O7  (heptose),  which  are  best  included  in  this  group. 


THE  GLUCOSES 


The  glucoses  have  a  sweet  taste,  though  less  sweet  than 
cane-sugar ;  they  are  easily  soluble  in  water,  and  at  once 
reduce  Fehling's  solution  (p.  62)  ;  they  also  readily  ferment 
under  the  influence  of  yeast.  The  various  glucoses  differ 
from  one  another  in  crystalline  form,  in  their  solubility  in 
various  reagents,  and  in  other  properties  ;  their  isomerism 
cannot  be  satisfactorily  accounted  for  by  the  ordinary  theories 
of  the  structure  of  carbon  compounds,  and  its  fuller  explana- 
tion is  undoubtedly  to  be  found  in  the  application  of  Van't 
Hoff's  theory  of  the  tetrahedral  carbon  atom  (see  p.  108). 
In  view  of  this,  special  importance  is  attached  to  the  varying 
power  of  the  different  glucoses  to  rotate  the  plane  of  polarisa- 
tion of  light. 

Chemically  the  glucoses  are,  in  the  first  place,  alcohols ; 
they  (at  least  those  of  the  formula  C6H12O6)  contain  five  OH 
groups  (each  of  which  can  be  replaced  by  acetyl  upon  treat- 
ment with  acetic  anhydride,  see  p.  79).  In  the  second  place, 
the  reducing  power  of  the  glucoses  leads  to  the  conclusion  that 
they  are  aldehydes  or  ketones  as  well  as  alcohols  ;  they  contain 
therefore  five  OH  groups  and  one  CHO  or  CO  group. 

This  CHO  or  CO  group  can  be  converted  by  reduction  into 
a  sixth  alcohol  group — CH2OH  or  CHOH.  We  thus  obtain 
by  reduction  of  a  glucose  a  hexhydric  alcohol,  which  may  be 
regarded  as  the  parent  of  that  particular  glucose.  The  alcohol 
obtained  has  in  each  case  the  formula  C(.H8(OH)6,  but  while 
two  of  the  glucoses  (dextrose  and  levulose)  yield  mannitol,  a 
third  (galactose)  yields  an  isomer  of  that  substance,  viz.  dulcitol. 

Mannitol  is  also  contained  in  manna,  and  is  present  in  many  plants, 
as  is  also  the  isomeric  dulcitol.  Both  are  derivatives  of  normal  hexane, 
C6H]4,  and  their  isomerism  is  to  be  explained  by  Van't  Hoff's  theory  of 
the  tetrahedral  carbon  atom. 

Dextrose,  C0H12O6,  is  present  in  many  fruits,  and  also  in 
honey.  It  rotates  the  plane  of  polarisation  to  the  right. 

Dextrose  is  formed  in  the  hydrolysis  (splitting  up  of  com- 
pounds by  addition  of  water)  of  many  other  carbohydrates.  The 
hydrolysis  is  effected  by  heating  with  water  under  pressure,  or 
more  easily  by  boiling  with  a  dilute  mineral  acid.  Thus  we 
have  the  following  reactions  : — 

Cane-sugar  +  H2O  =  Dextrose  +  Levulose 
Starch          +  HJ3  =  Dextrose 


DEXTROSE  AND  LEVULOSE 


The  dextrose  of  commerce  is  prepared  by  treating  starch  with  boiling 
dilute  sulphuric  acid  under  pressure.  The  solution  is  freed  from  sulphuric 
acid  by  adding  calcium  carbonate  and  filtering  from  the  calcium  sulphate ; 
it  is  then  evaporated,  and  leaves  a  tough  non-crystalline  mass. 

Levulose,  C6H12O6,  occurs  along  with  dextrose  in  fruits 
and  honey,  and  the  "invert-sugar"  obtained  by  the  action  of 
dilute  acids  on  cane-sugar  is  a  mixture  of  equal  parts  of  dex- 
trose and  levulose. 

Levulose  rotates  the  plane  of  polarisation  more  strongly 
than  dextrose,  but  to  the  left. 

The  dextrose  and  levulose  which  are  present  together  in  honey  and  in 
invert-sugar  can  be  partially  separated  by  washing  the  mixture  with  cold 
alcohol.  The  more  soluble  levulose  is  thus  removed  dissolved  in  the 
alcohol,  and  the  less  soluble  dextrose  remains  for  the  most  part  un- 
dissolved. 


Galactose,  C6H12O0, 


is  formed  along  with  dextrose  in  the 
hydrolysis  of  milk-sugar  : 

Milk-sugar  -f  H2O  =  Dextrose  +  Galactose. 

Unlike  dextrose  and  levulose,  galactose  does  not  ferment  with 
yeast.      When  reduced  it  yields  dulcitol  : 


Rotation  of 
polarised  light. 

Action  of  yeast. 

Reduction 
product. 

Dextrose 

To  right 

Ferments 

Mannitol 

Levulose 

To  left 

Ferments  less 
rapidly  than 
glucose 

Mannitol 

Galactose 

To  right 

Does  not  fer- 
ment 

Dulcitol 

CANE-SUGAR  GROUP  OR  BIOSES 

The  members  of  this  group  are  made  up  of  two  molecules 
of  glucose  united  together  with  elimination  of  a  molecule  of 


HYDROLYSIS  OF  SUGAR 


CHAP. 


water.  When  hydrolysed  (see  above)  they  take  up  water  to 
form  two  molecules  of  glucose.  The  formula  is  Cj^H^Ojj, 
and  the  following  table  indicates  the  relation  of  the  most  im- 
portant members  of  the  group  to  the  glucoses  : 

Cane-sugar  -f  H9O  =  Dextrose  +  Levulose 
Milk-sugar  +  H2O  =  Dextrose  +  Galactose 
Maltose       +  H2O  =  Dextrose  +  Dextrose 

The  Bioses  are  not  so  strong  reducing  agents  as  the  Glucoses. 
None  of  them  is  able  to  reduce  Fehling's  solution  in  the  cold, 


FIG.  32. — Sugar-cane. 

Yield  of  canes  per  acre,  30-40  tons, 

containing  about  5  tons  of  sugar. 


FIG.  33. — Sugar-beet. 
Yield  of  beet  per  acre,  15-20  tons, 
containing  about  2  tons  of  sugar. 


but  maltose  does  so  readily  when  heat  is  applied, 
reduce  it  only  very  slowly  even  when  boiled. 


The  others 


CANE-SUGAR  123 


Cane-sugar,  C12H.22OU,  is  present  in  the  sap  of  many 
plants,  especially  the  sugar-cane  and  the  beet-root.  In  order 
to  obtain  the  sugar  the  sap  is  extracted  either  by  crushing 
and  pressure,  or  by  cutting  into  thin  slices  and  soaking  in 
water.  The  juice  is  purified  by  filtration  and  other  processes, 
and  is  then  evaporated  in  vacuum-pans  until  sugar  separates 
out  from  the  juice  on  cooling. 

A  portion  only  of  the  sugar  is  thus  obtained  in  the  crystal- 
line state,  the  remainder  is  left  in  the  form  of  a  thick  syrup 
after  the  crystals  have  been  removed,  and  the  sugar  in  it  is 
prevented  by  impurities  from  crystallising.  These  "  molasses  " 
may  either  be  fermented  and  converted  into  spirit  (rum),  or 
by  certain  modern  processes  the  impurities  may  be  separated 
and  the  sugar  obtained  in  the  solid  form. 

In  one  of  these,  the  diffusion  process,  the  syrup  is  put  into 
what  are  practically  huge  bags  made  of  parchment  paper,  and 
these  bags  are  placed  in  pure  water.  The  sugar  of  the  molasses 
diffuses  through  the  pores  of  the  parchment  paper  faster  than 
the  impurities  which  are  mixed  with  it,  and  there  is  thus  ob- 
tained in  the  liquor  surrounding  the  bags  a  solution  of  sugar 
sufficiently  pure  to  yield  a  crystalline  product  on  evaporation. 

The  other  process  depends  on  the  formation  of  a  nearly 
insoluble  compound  with  lime,  having  the  composition 
C12H.,.2On  •  3CaO.  This  is  precipitated  from  the  molasses 
by  addition  of  powdered  quick-lime,  and  after  being  purified 
by  washing,  is  decomposed  by  passing  a  stream  of  CO2  through 
water  with  which  the  "  lime  saccharate  "  is  mixed.  The  lime 
is  separated  as  calcium  carbonate,  and  a  weak  syrup  of  pure 
sugar  is  obtained,  which  can  readily  be  concentrated  by  evapora- 
tion. 

Cane-sugar  crystallises  in  large  monoclinic  prisms  (sugar- 
candy).  It  is  very  soluble  in  water,  but  is  easily  crystallised 
from  its  solutions  by  evaporation  unless  the  presence  of  im- 
purities interferes.  Solutions  rotate  the  plane  of  polarisation 
of  light  to  the  right.  On  boiling  with  a  dilute  acid  cane-sugar 
is  converted  into  a  mixture  of  dextrose  and  levulose  : 

C12H22°11  +  H2°  =  C6H12°6  +  C6H12°0  '> 
Cane-sugar.  Dextrose.        Levulose. 

and  as  levulose  has  a  higher  rotatory  power  than  dextrose,  the 


124  MILK-SUGAR 


mixture  of  the  two  thus  obtained  rotates  to  the  left  ;  this  in- 
version is  the  origin  of  the  name  invert-sugar,  which  is  applied 
to  the  product  thus  obtained. 

When  heated,  cane-sugar  melts  at  160°  C.,  and  if  then 
allowed  to  cool  solidifies  to  a  semi-transparent  mass  ("  barley- 
sugar"),  which  is  devoid  of  crystalline  structure.  On  long 
standing  this  gradually  becomes  crystalline  again.  If  heated 
to  about  200°  C.,  cane-sugar  is  changed  into  a  brown  sub- 
stance known  as  "caramel,"  or  "burnt-sugar,"  which  is  used 
as  colouring  matter  by  cooks. 

Cane-sugar  when  subjected  to  the  influence  of  the  growing 
yeast-plant  is  first  changed  into  a  mixture  of  dextrose  and 
levulose.  As  soon  as  any  considerable  quantity  of  these 
glucoses  has  been  formed  alcoholic  fermentation  sets  in,  fol- 
lowing chiefly  the  equation 

C6H1206  2C2H60     +     2C02. 

Glucose.  Ethyl  alcohol. 

Milk-sugar,  C12H22On,  is  present  in  milk,  and  remains 
dissolved  in  the  whey  after  the  casein  has  been  separated  in 
the  manufacture  of  cheese.  It  is  less  soluble  in  water  than 
cane-sugar,  and  much  less  sweet.  Its  solutions  rotate  the 
plane  of  polarisation  to  the  right. 

Milk-sugar  does  not  easily  ferment  with  yeast,  but  by  the 
action  of  certain  bacteria  it  readily  ferments  with  production 
of  lactic  acid  : 

C12H22011  +  H20  =  4C3H603. 
Milk-sugar.  Lactic  acid. 

This  is  the  change  which  occurs  when  milk  turns  sour. 

As  has  been  already  mentioned,  the  hydrolysis  of  milk- 
sugar  yields  dextrose  and  galactose  : 

C12H220U  +  H20  =  C6H1206  +  C6H1206. 

Milk-sugar.  Dextrose.       Galactose. 

Maltose,  C12H92O11,  is  contained  in  malt,  having  been 
produced  by  the  action  of  a  certain  ferment — diastase— upon 
the  starch  present  in  the  barley  or  other  grain  which  has  been 
malted. 


xvin  STARCH  125 

Upon  hydrolysis— boiling  with  a  dilute  acid — maltose  yields 
dextrose  only  : 

Maltose.  Dextrose. 

It  resembles  the  glucoses  much  more  closely  than  do  cane- 
and  milk-sugar  ;  thus  it  ferments  quickly  (i.e.  without  previous 
conversion  into  glucoses)  with  yeast,  and  reduces  Fehling's 
solution  readily  when  warmed  with  it. 

THE  CELLULOSE  GROUP 

In  this  group  we  include  a  number  of  carbohydrates  whose 
constitution  is  less  understood  even  than  that  of  the  glucoses 
and  bioses.  It  is  very  probable  that  their  molecular  weights 
are  very  high,  but  it  has  not  yet  been  found  possible  to  deter- 
mine their  real  values,  and  we  can  only  give  the  empirical 
formulae.  The  most  important  members  of  the  group  are 
starch,  dextrin,  and  cellulose— all  C6H10O5 — and  the  gums, 
whose  probable  formula  is  C5H10O5. 

Starch,  C6H10O5,  is  the  form  in  which  very  many  plants 
store  up  their  reserves  of  food.  It  is  largely  present  in  many 
roots  and  seeds,  as  the  following  table  will  show  : — 

Per  cent 
of  starch. 

Potatoes  .  .'  .  20 
Wheat,  maize  .  •  .  60 
Rice  .  .  .  .  70 

Starch  is  also  a  very  important  food  for  animals  ;  and  arrow- 
root, sago,  and  tapioca  are  nearly  pure  starch  extracted  from 
certain  plants.  The  separation  of  starch  from  the  other  con- 
stituents of  the  plants  is  effected  by  beating  them  with  water 
into  a  thin  pulp,  which  is  then  filtered  through  fine  sieves. 
The  fibrous  matter  is  kept  back,  and  the  milky  liquid  which 
runs  through  deposits  the  starch  on  standing.  This  is  then 
collected  and  dried. 

Starch  is  really  insoluble  in  water,  but  when  boiled  with  it 
yields  a  liquid  which  can  be  filtered  without  separating  the 
starch.  This  is,  however,  merely  present  in  a  very  fine  state 


i26  CELLULOSE 


of  subdivision,  forming  what  is  called  a  "  colloidal  "  solution. 
The  starch  in  it  is  unable  to  pass  through  a  membrane  of 
parchment  paper,  whereas  substances  in  real  solution  are  able 
slowly  to  diffuse  through  such  a  membrane.  Neither  has  the 
starch  any  effect  on  the  freezing-point  of  the  water  containing 
it  (see  p.  1  6). 

When  heated  to  about  200°  C.,  starch  is  changed  into  dex- 
trin. 

Very  characteristic  of  starch  is  the  intensely  blue  compound 
which  it  forms  with  iodine.  This  furnishes  a  very  sensitive 
test  either  for  starch  or  for  free  iodine.  The  blue  colour  dis- 
appears when  sufficient  heat  is  applied,  but  reappears  on  cool- 
ing. 

Dextrin,  C6H1QO5,  is  obtained  by  simply  heating  starch  to 
about  200°  C.,  or  by  boiling  it  with  dilute  acids.  Dextrin  is 
used  as  a  substitute  for  gum.  It  is  not  coloured  blue  by 
iodine. 

Cellulose,  C6H1QO5,  is  the  chief  constituent  of  the  cell- 
walls  of  plants  ;  wood  is  chiefly  cellulose,  while  cotton-wool 
and  filter-paper  are  nearly  pure  cellulose.  This  is  insoluble 
in  all  ordinary  solvents,  but  concentrated  sulphuric  acid 
dissolves  it,  and  the  solution  when  diluted  and  boiled  yields 
first  dextrin  and  then  dextrose. 

The  exact  chemical  constitution  of  cellulose  is  matter  for 
future  investigation.  It  appears,  however,  to  contain  three- 
fifths  of  its  oxygen  in  the  form  of  hydroxyl  groups  OH,  as  \ve 
find  that  by  the  action  of  acids  ethereal  salts  of  cellulose  may 
be  prepared  in  which  three  acid  groups  are  introduced  into 
the  formula  C6H10O5  ;  the  real  molecular  formula  of  cellulose 
is  unknown,  but  it  is  more  convenient  to  regard  these  ethereal 
salts  as  derived  from  the  doubled  formula  C12H2QO10,  in  which, 
of  course,  there  are  six  hydroxyls. 

The  most  important  of  these  salts  are  the  nitrates  ;  these 
are  prepared  by  treating  cellulose  (cotton-wool)  with  strong 
nitric  acid,  the  action  being  aided  by  the  addition  of  concen- 
trated sulphuric  acid.  When  the  strongest  acids  are  employed 
the  product  obtained  is  gun-cotton,  which  is  found  to  be 
cellulose  hexa-nitrate  : 


=  C12H14°4(N°3)(i  +  6H2°' 
Cellulose.  Gun-cotton. 


xvin  GUN-COTTON  127 

This  material  is  a  violent  explosive,  and  is  prepared  by 
steeping  cotton-wool  for  a  few  minutes  in  a  cold  mixture  of  the 
strongest  nitric  acid  with  two  or  three  times  its  weight  of 
concentrated  sulphuric  acid.  When  thoroughly  freed  from 
acid  by  washing,  gun-cotton  is  comparatively  quite  safe  to 
handle,  and  may  even  be  set  fire  to  without  anything  more 
violent  than  a  rather  quick  combustion  taking  place ;  but 
when  subjected  to  the  shock  set  up  by  exploding  a  small 
charge  of  fulminate  embedded  in  the  gun-cotton,  the  molecules 
of  the  latter  break  down  suddenly,  and  a  powerful  explosion 
results  ;  the  rearrangement  of  atoms  which  then  occurs  may 
be  roughly  represented  by  the  following  equation  : 

Ci2Hu°4(N°3)c  =  3N2  +  7H.O  +  9CO  +  3C02. 

Gun-cotton. 

Pyroxylin  is  a  less  highly  nitrated  cellulose,  chiefly  the 
tetra-nitrate  ;  it  is  prepared  with  a  somewhat  weaker  nitric 
acid.  Its  solution  in  a  mixture  of  alcohol  and  ether  is  the 
collodion  which  is  largely  used  in  photography  (wet -plate 
process),  and  in  surgery  for  covering  wounds  with  a  thin 
flexible  film  which  prevents  access  of  air. 


QUESTIONS  ON  CHAPTER  XVIII 

1.  What  are  the  chief  members  of  the  group  of  "glucoses"  ;  what  is 
their  formula,  and  what  explanation  of  their  isomerism  may  be  advanced  ? 

2.  What    is  the  action   upon  dextrose  of  (a)  Fehling's   solution,    (l>) 
yeast,  (c)  acetic  anhydride? 

3.  What  two  substances  are    present   in   largest   quantity   in   honey? 
How  do  they  differ  from  one  another  ? 

4.  What   products  are  obtained   by  the  action  of  boiling  dilute  acids 
upon  (a)  cane-sugar,  (b]  milk-sugar,  (c)  maltose? 

5.  Describe   the   preparation  of  gun-cotton,   and   give   its   chemical 
constitution. 


CHAPTER    XIX 
UREA  AND   URIC  ACID 

Urea,  CO(NH0)t>,  is  one  of  the  most  important  waste- 
products  of  the  animal  economy  ;  the  food  which  animals 
consume  is  converted  during  its  passage  through  the  blood 
and  tissues  of  the  body  chiefly  into  urea,  carbon  dioxide,  and 
water.  The  urea  is  secreted  along  with  a  considerable 
proportion  of  the  water  by  the  kidneys,  and  it  was  from  urine 
that  this  substance  was  first  obtained  in  1773. 

Urea  thus  obtained  and  afterwards  carefully  purified  was 
found  by  analysis  to  have  the  composition  CON2H4.  This  is 
also  the  composition  of  ammonium  cyanate,  (NH4)NCO,  and 
though  that  body  is  itself  quite  distinct  from,  and  isomeric 
with',  urea,  in  1828  Wohler  made  the  very  important  discovery 
that  a  solution  of  ammonium  cyanate  in  water  yields  urea  on 
evaporation.  The  great  readiness  with  which  this  change 
occurs  while  indicating  that  urea  is  the  more  stable  of  the  two 
isomers  also  seems  to  show  that  they  are  not  very  different  in 
constitution.  Several  synthetical  methods  which  have  since 
been  discovered  for  the  preparation  of  urea  show  that  it  may 

be  regarded  as  the  amide  of  carbonic  acid,  CO-^,^,     '2.     Thus 

just  as  the  amide  of  acetic  acid  (acetamide)  can  be  got  by  the 
action  of  ammonia  on  acetyl  chloride  : 

CH.,.COC1  +  NH,  =  CH.,.  CONH.,  +  HC1, 

O  O  o  — 

Acetyl  chloride.  Acetamide. 

so  urea  can  be  obtained  by  the  action  of  ammonia  on  carbonyl 
chloride  COCL, : 


CHAP,  xix  PREPARATION  OF  UREA  129 

COC12  +  2NH3  =  CO(NH2)2  +  2HC1. 
Carbonyl  Carbamide 

chloride.  or  urea. 

The  most  convenient  way  of  preparing  urea  is  by 
evaporating  a  solution  in  water  of  potassium  cyanate  and 
ammonium  sulphate  mixed  in  equivalent  proportions ;  the 
potassium  cyanate  is  easily  obtained  by  heating  potassium 
ferrocyanide  with  manganese  dioxide. 

EXPT.  19.  Heat  four  parts  potassium  ferrocyanide  with  two  parts  of 
MnOa  in  a  clay  crucible,  extract  the  cooled  melt  with  water,  add  three  parts 
of  ammonium  sulphate,  and  evaporate  to  dryness.  Potassium  sulphate 
and  urea  are  left,  and  may  be  separated  by  extraction  with  alcohol,  in 
which  the  urea  only  is  soluble. 

Urea  crystallises  in  rhombic  prisms  which  are  easily 
soluble  in  water.  It  is  a  mon-acid  base,  and  forms  salts  of 
which  the  nitrate  CON9H4  .  HNO3  is  very  sparingly  soluble 
in  water  containing  nitric  acid,  and  may  therefore  be  used  as 
a  means  of  detecting  urea  in  solutions  not  too  dilute. 

Like  other  amides  urea  is  decomposed  on  boiling  with 
dilute  alkalies,  and  ammonia  is  given  off: 

CO(NH2)2  +  H2O  =  CO,  +  2NH3. 
Urea. 

Another  important  reaction  of  urea  is  its  behaviour  when 
treated  with  bromine  and  caustic  soda  (sodium  hypobromite)  ; 
it  is  then  oxidised  to  CO0  and  water  while  the  nitrogen  is 
given  off  as  such  : 

CON2H4  +  3NaOBr  =  CO2  +  2H2O  +  N2  +  aNaBr. 

EXPT.  20.  Put  some  solution  of  urea  in  a  boiling  tube,  add  caustic 
soda  and  bromine  water  ;  notice  that  a  gas  is  given  off  in  bubbles,  and  by 
testing  with  a  match  show  that  it  puts  out  the  flame.  (The  gas  cannot 
be  CO0,  because  the  solution  contains  excess  of  alkali. )  The  experiment 
can  be  so  arranged  that  the  nitrogen  may  be  collected  and  measured  ; 
from  its  amount  that  of  the  urea  can  be  calculated,  and  on  this  a  method 
for  estimating  urea  is  based.  It  must,  however,  be  remembered  that 
many  other  nitrogen  compounds  also  give  off  their  nitrogen  when  treated 
with  a  hypobromite. 

Uric  Acid,  C5H4N4O3  (5443),  may  be  regarded  as  a  less 
completely  oxidised  result  of  the  digestive  and  absorptive 


130  URIC  ACID  CHAP,  xix 

processes  than  urea.  Uric  acid  is  present  only  in  small 
quantity  in  the  urine  of  man,  but  in  certain  abnormal  con- 
ditions of  the  body  it  is  more  largely  produced,  usually  with 
very  unpleasant  consequences.  Both  uric  acid  and  its  salts  are 
soluble  only  with  difficulty  in  water,  hence  they  are  difficult  to 
remove  when  produced  in  the  body  in  any  considerable 
quantity,  and  either  gout,  in  which  accumulations  of  urates 
occur  in  various  parts  of  the  body,  or  other  disturbances  of 
the  healthy  procedure  occur. 

In  some  animals,  on  the  other  hand,  especially  birds  and 
reptiles,  uric  acid  is  largely  secreted,  and  both  guano  (which 
is  produced  by  sea-birds)  and  the  excreta  of  serpents  contain 
considerable  quantities,  and  from  either  of  these  sources  the 
acid  may  readily  be  prepared. 

If  guano  is  used  it  is  best  boiled  with  a  solution  of  borax  (i  to  100  of 
water),  in  which  uric  acid  is  fairly  soluble.  Addition  of  hydrochloric  acid 
to  the  filtered  solution  precipitates  the  bulk  of  the  uric  acid  present. 

Uric  acid  is  a  white  powder,  soluble  only  very  slightly  in 
pure  water,  but  more  readily  in  water  containing  certain  salts 
in  solution.  It  is  a  weak  di-basic  acid,  but  the  best 
characterised  salts  are  these  with  only  one  equivalent  of  metal, 
such  as  C5H3KN4O3,  potassium  urate  ;  they  are  all  very 
slightly  soluble  in  water. 

To  test  a  substance  for  the  presence  01  uric  acid  a  few 
drops  of  dilute  nitric  acid  are  added  to  it,  and  then  evaporated 
on  the  water  bath ;  if  a  yellow  residue  is  left  which  is  coloured 
purple  by  addition  of  ammonia,  we  may  conclude  that  uric 
acid  was  contained  in  the  substance  examined. 


QUESTIONS  ON  CHAPTER  XIX 

1.  How  can  urea  be  prepared  from  potassium  ferrocyanide  ? 

2.  What    is    the   action    upon   urea   of   (a)   sodium    hypobromite,    (l>) 
boiling  caustic  soda  solution  ? 

3.  What  products  are  formed   by  the   action   of  ammonia  upon   (a) 
carbonyl  chloride,  (b)  acetyl  chloride  ? 

4.  From  what  sources  can  uric  acid  be  obtained  ?     Write  down  the 
formulae  of  uric  acid  and  of  potassium  urate. 


CHAPTER    XX 
THE  CYANOGEN   COMPOUNDS 

THE  cyanogen  compounds  include  a  large  number  of  sub- 
stances which  are  alike  in  containing  the  monovalent  radicle 
cyanogen  -  CN,  made  up,  as  its  formula  shows,  of  one  atom 
each  of  tetravalent  carbon  and  trivalent  nitrogen:  -C  =  N. 
Sometimes  the  special  symbol  Cy  is  used  to  denote  the 
cyanogen  radicle. 

The  starting-point  in  the  preparation  of  the  various  cyanogen 
compounds  is  potassium  ferrocyanide,  or  "  yellow  prussiate  of 
potash,"  but  as  the  composition  of  this  substance  is  somewhat 
complex  it  is  better  to  begin  with  other  and  simpler  bodies. 

Cyanogen,  C2N2,  a  compound  whose  molecule  is  formed 
of  two  cyanogen  radicles  united  together  (just  as  free  chlorine 
or  hydrogen  is  C12  or  H2),  is  made  by  heating  mercuric 
cyanide  to  a  red  heat,  when  it  decomposes  into  mercury  and 
cyanogen  : 

Hg(CN)2=Hg  +  C2N2. 

It  is  a  poisonous  gas  with  a  characteristic  smell,  and  burns  in 
air  with  a  peculiar  ("peach-blossom  colour")  flame;  its  mix- 
ture with  oxygen  explodes  violently  on  application  of  a  flame  : 


Cyanogen  is  readily  soluble  in  water,  and  must  therefore  be 
collected  over  mercury. 

Chemically  cyanogen  behaves  as  the  "nitrile"  of  oxalic  acid.  It  can 
be  obtained  from  the  amide  of  oxalic  acid  —  oxamide  (CONHaJa  —  by  with- 
drawing water  (action  of 


132  HYDROCYANIC  ACID  CHAP. 

CONH2 
CONH3 

and  the  inverse  reaction  can  be  brought  about  by  allowing  a  solution  of 
cyanogen  in  water  or  dilute  acid  to  stand  for  several  days  : 

C2N2  +  2H2O  =  C2O2(NH2)2. 

Compare  the  relation  of  methyl  cyanide  (acetonitrile)  CH3CN  to  aceta- 
mide,  pp.  89  and  134. 

Hydrocyanic  Acid,  HCN,  or  "  Prussic  Acid,"  is  now 
most  largely  prepared  by  the  action  of  boiling  dilute  sulphuric 
acid  upon  potassium  ferrocyanide  : 

2K4FeCy(.  +  3H2SO4  =  3K2SO4  +  K2Fe2Cy6  +  6HCN. 

By  this  method  a  solution  of  hydrocyanic  acid  in  water  is 
obtained,  from  which  the  anhydrous  acid  can  be  prepared  by 
passing  the  vapours  through  tubes  containing  calcium  chloride 
or  other  suitable  dehydrating  agent. 

An  older  method  of  preparing  the  dilute  acid  is  from 
amygdalin,  a  compound  present  in  bitter  almonds,  laurel 
leaves,  and  parts  of  various  other  plants.  The  amygdalin, 
when  the  leaves,  etc.,  steeped  in  water,  are  exposed  to  the  air, 
usually  undergoes  a  fermentation  which  results  in  the  forma- 
tion of  hydrocyanic  acid,  oil  of  bitter  almonds  (benzaldehyde, 
see  Part  II.),  and  sugar.  The  hydrocyanic  acid  is  then  easily 
obtained  by  distillation. 

The  salts  of  hydrocyanic  acid — the  cyanides — are  formed 
whenever  carbon  and  nitrogen  come  in  contact  with  a  strong 
base  at  a  high  temperature.  The  nitrogen  may  be  supplied 
in  the  free  state,  or  may  be  present  in  combination  with  other 
elements.  Thus  potassium  cyanide  is  formed  when  nitrogen 
is  passed  over  a  heated  mixture  of  potash  and  powdered  coal, 
and  cyanides  are  always  formed  in  distilling  coal  for  the  manu- 
facture of  coal-gas  from  the  joint  interaction  of  ammonia  with 
the  nitrogen  and  carbon  present  in  the  coal.  The  two  chief 
sources  of  the  cyanides  (which  are  largely  manufactured  for 
use  in  electro-plating,  for  making  Prussian  blue,  and  other  pur- 
poses) are  to  be  associated  with  this  method  of  formation. 
They  are — 


xx  SOURCES  OF  THE  CYANIDES  133 

i  .  Potassium  ferrocyanide,  yellow  prussiate  of  potash,  which 
is  made  by  carbonising  nitrogenous  animal  refuse  (horn,  leather 
scraps,  etc.)  and  heating  the  residue,  which,  though  chiefly 
carbon,  still  contains  a  considerable  proportion  of  nitrogen, 
with  caustic  potash  and  iron  filings. 

2.  An  important  source  of  cyanides  is  now  found  in  the 
by-products  of  the  manufacture  of  coal-gas.  The  cyanides 
formed  during  the  destructive  distillation  of  the  coal  are  re- 
tained chiefly  in  the  lime-purifiers,  and  are  extracted  from  the 
spent  lime  by  treatment  with  quicklime  at  steam  heat.  This 
decomposes  the  insoluble  cyanogen  compounds  present  in  the 
spent  lime,  and  converts  them  into  soluble  calcium  ferro- 
cyanide. 

Cyanides  are  now  also  recovered  from  the  by-products  of 
other  manufactures  —  blast-furnaces,  coke-ovens,  etc. 

Other  reactions,  of  theoretical  interest  only,  by  which  hydrocyanic  acid 
or  its  salts  can  be  obtained,  are  — 

i.  The  action  of  the  electric  discharge  upon  a  mixture  of  acetylene  and 
nitrogen  : 


2.    The  action  of  ammonia  upon  chloroform  (in  the  presence  of  caustic 
potash)  : 

NH3  +  CHC1,  =  3HC1  +  HCN. 

Pure  hydrocyanic  acid,  free  from  water,  is  a  colourless  volatile 
liquid,  with  a  strong  smell  and  intensely  poisonous  properties. 
It  is  a  well-marked  acid,  but  its  salts  with  the  alkaline  metals 
are  easily  decomposed,  even  carbon  dioxide  being  sufficiently 
powerful  to  liberate  the  acid  from  potassium  or  ammonium 
cyanides  ;  hence  it  is  that  these  substances  always  smell  of 
hydrocyanic  acid  when  exposed  to  the  air.  The  cyanides  of 
the  heavy  metals  are,  on  the  other  hand,  much  more  stable, 
silver  cyanide  being  unattacked  even  by  the  strong  acids. 

The  solution  of  hydrocyanic  acid  in  water  readily  decom- 
poses with  formation  of  ammonium  formate  and  other  sub- 
stances. A  similar  change  occurs  more  readily  by  the  action 
of  dilute  mineral  acids,  showing  that  hydrocyanic  acid  may  be 
regarded  as  the  nitrile  of  formic  acid  : 

HCN        +      2H2O    =    HC02H    +    NH3, 

Hydrogen  cyanide.  Formic  acid. 

with  which  compare 


134  THE  CYANIDES 


CH3CN      +    2H2O  -  CH3  .  CO2H  +  NH3. 
Methyl  cyanide  Acetic  acid, 

or  "  acetonitrile." 

Potassium  Cyanide,  KCN,  is  manufactured  by  heating 
potassium  ferrocyanide  in  iron  vessels  until  decomposition 
occurs  according  to  the  equation  : 

K4FeC0N6  =  4KCN  +  FeC2  +  N2. 

The  potassium  cyanide  is  separated  from  the  iron-carbide  by 
extracting  the  mass  with  water  ;  the  solution  is  evaporated, 
and  the  residue,  after  being  fused,  is  brought  into  market  in 
lumps  or  sticks. 

Perfectly  pure  potassium  cyanide  is  best  obtained  by  passing  vapours 
of  HCN  into  a  solution  of  KOH  in  alcohol. 

Potassium  cyanide  is  very  soluble  in  water,  and  is  extremely 
poisonous.  It  is  largely  used  in  electro-plating  for  preparing 
the  solutions  of  gold  or  silver,  and  in  the  gold-fields  for  dis- 
solving the  gold  from  the  quartz  containing  it.  It  is  used  in 
the  laboratory  as  a  reducing  agent  in  blow-pipe  work. 

Mercuric  Cyanide,  Hg(CN)2,  is  prepared  by  boiling 
Prussian  blue  with  water  and  mercuric  oxide,  or  by  dissolving 
mercuric  oxide  in  hydrocyanic  acid.  It  is  fairly  soluble  in 
water,  is  very  poisonous,  and  forms  good  crystals.  It  does 
not  evolve  any  perceptible  amount  of  hydrocyanic  acid  when 
treated  with  cold  dilute  sulphuric  acid,  but  gives  it  off  slowly 
on  boiling. 

Silver  Cyanide,  AgCN,  is  obtained  as  a  white  precipitate 
when  a  solution  of  potassium  cyanide  is  added  to  one  of  silver 
nitrate.  It  is  insoluble  in  acids,  but  dissolves  readily  in  excess 
of  the  solution  of  KCN  owing  to  the  formation  of  a  soluble 
double  salt  AgCN  .  KCN. 

On  this  is  based  a  method  for  the  quantitative  estimation  of  soluble 
cyanides  ;  standard  solution  of  silver  nitrate  is  added  to  the  solution  of  the 
cyanide  until  a  permanent  white  precipitate  just  begins  to  form.  When 
this  occurs,  one  molecule  of  AgNO3  has  been  added  for  every  two  mole- 
cules of  the  cyanide  present  : 

.  KCN  +  KNO3. 


XX  THE  FERROCYANIDES  135 

Double  Cyanides.  —  In  the  double  salt  just  referred  to  — 
AgCN  .  KCN—  we  have  an  example  of  the  marked  tendency 
shown  by  various  cyanides  of  different  metals  to  combine  to 
form  double  cyanides.  In  some  of  these  double  salts  the  com- 
bination is  only  loose  and  is  readily  broken,  while  their  pro- 
perties are  not  fundamentally  different  from  those  of  simple 
cyanides.  But  in  another  important  class  of  double  cyanides 
the  combination  is  so  complete  that  the  essential  properties  of 
the  constituent  salts  entirely  disappear  in  the  double  cyanide 
formed  by  their  union. 

Potassium  Ferrocyanide,  K4FeCy6,  is  such  a  double 
cyanide.  Its  formula  may  be  regarded  as  showing  it  to  be 
made  up  of  4KCy-fFeCy9,  four  molecules  of  potassium 
cyanide  with  one  of  ferrous  cyanide,  but  in  reality  neither  the 
cyanogen  group,  nor  the  iron  contained  in  the  ferrocyanide 
can  be  detected  by  their  ordinary  reactions.  The  ferrocyanide 
is  almost  non-  poisonous  in  comparison  with  the  intensely 
poisonous  nature  of  the  soluble  simple  cyanides,  and  the  iron 
in  it  is  not  precipitated  by  ammonium  sulphide. 

Potassium  ferrocyanide  is  largely  manufactured  to  serve  as 
a  starting-point  for  the  preparation  of  Prussian  blue  and  other 
cyanogen  compounds.  It  is  known  commercially  as  yellow 
prussiate  of  potash,  and  is  made  by  heating  in  shallow  iron 
pans  a  mixture  of  charred  nitrogenous  refuse  (horn,  skin,  etc.) 
with  potash  and  iron  filings.  The  ferrocyanide  is  extracted 
with  water  from  the  fused  residue  and  purified  by  recrystallisa- 
tion.  It  forms  large  tabular  crystals  of  an  amber  colour.  It 
dissolves  easily  in  water,  and  the  solution  gives  characteristic 
precipitates  with  solutions  of  several  metallic  salts,  e.g.  with 
copper  sulphate  solution  a  brown  precipitate  of  copper  ferro- 
cyanide is  obtained  : 


K4FeCy6  +  2CuSO4  =  2K2SO4  +  Cu2FeCy6. 
Potassium  Copper 

ferrocyanide.  ferrocyanide. 

When  a  strong  acid,  (HC1),  is  added  to  the  concentrated 
solution  of  potassium  ferrocyanide,  a  white  precipitate  of 
ferrocyanic  acid,  H4FeCy(5,  is  produced  : 

K4FeCy6  +  4HC1  =  4KC1  +  H4FeCy6. 


136 


PRUSSIAN   BLUE 


CHAP. 


The  complex  radicle,  Fe(GN)(.  or  FeCy6,  which  is  present 
in  ferrocyanic  acid  and  the  ferrocyanides,  carries  the  name 
"  ferrocyanogen." 

Potassium  Ferricyanide,  K.^FeCy,.,  is  formed  by  oxidis- 
ing a  solution  of  the  ferrocyanide  by  means  of  chlorine  : 


2K4FeCy0  +  C12  =  2KC1 


2KaFeCy6. 


It  may  be  regarded  as  built  up  from  three  molecules  of  KCN 
with  one  of  ferric  cyanide  FeCy,,,  but  just  as  is  the  case  with 
the  ferrocyanide  the  properties  of  the  compound  are  essentially 
different  from  those  of  the  simple  cyanides. 

Potassium  ferricyanides  is  the  commercial  "  red  prussiate 
of  potash,"  and  forms  deep-red  crystals. 

Iron  Salts  and  the  Ferro-  and  Ferricyanides.— 
The  reactions  between  solutions  of  iron  salts  and  ferro-  or  ferri- 
cyanides are  of  importance  in  analytical  chemistry,  and  for  the 
thorough  understanding  of  the  composition  of  Prussian  blue. 
They  are  best  shown  in  a  tabulated  form  : 


Solution  used. 

Potassium  Ferrocyanide. 
K4FeCy6. 

Potassium  Ferricyanide. 
K3FeCytj. 

Ferrous  salt 

Light-blue  pp.  of  ferrous 
ferrocyanide,  which 
gradually  darkens  in 
the  air 

Dark  blue  pp.  of  ferrous 
ferricyanide  ;  Turn- 
bull's  blue 

Ferric  salt 

Dark  blue  pp.  of  ferric 
ferrocyanide  ;  Prus- 
sian blue 

No  pp.,  but  the  solution 
becomes  very  dark 
green  in  colour 

Prussian  Blue,  as  indicated  above,  is  chemically  to  be 
regarded  as  ferric  ferrocyanide,  Fe4(FeCy6)3  or  Fe7Cylg,  and 
is  formed  when  potassium  ferrocyanide  is  added  to  a  solution 
of  a  ferric  salt.  In  actual  practice  it  is  made  by  adding  the 
ferrocyanide  to  a  somewhat  oxidised  solution  of  ferrous  sul- 
phate, and  then  completing  the  oxidation  by  means  of  air. 

Cyanic    Acid,    HCNO.      It    has    been    mentioned    that 


THE  CYANATES  137 


potassium  cyanide  is  a  powerful  reducing  agent,  and  is  used 
as  such  in  analytical  chemistry  for  the  purpose  of  reducing  the 
metals  from  their  salts  by  fusion  with  sodium  carbonate  and 
the  cyanide.  In  such  reactions  the  potassium  cyanide  is  con- 
verted by  addition  of  oxygen  into  potassium  cyanate  : 

KCN  +  O  =  KCNO. 


The  cyanate  is  more  cheaply  prepared  by  heating  potassium 
ferrocyanide  with  an  oxidising  agent,  such  as  MnO2  or 
K2Cr2Or 

Potassium  Cyanate,  KCNO,  is  a  white  solid,  easily 
soluble  in  water.  The  solution  gradually  decomposes  when 
kept.  On  addition  of  an  acid  free  cyanic  acid  is  not  obtained, 
but  only  its  products  of  decomposition  with  water  —  ammonia 
and  carbon  dioxide  : 

HCNO  +  H9O  =  NH,  +  CO9. 

A  o  L 

Ammonium  Cyanate,  NH4CNO,  is  of  special  importance 
on  account  of  its  ready  transformation  into  urea,  CO(NH2)2, 
see  p.  128.  It  is  most  easily  obtained  in  solution  by  mixing 
strong  solutions  of  potassium  cyanate  (prepared  as  above)  and 
ammonium  sulphate.  The  difficultly  soluble  potassium  sul- 
phate will  separate  out  in  part  : 

2KCNO  +  (NH4)2SO4  -  K2SO4  +  2NH4CNO, 

and  the  solution  on  evaporation  yields  urea  along  with  some 
potassium  sulphate. 

Free  Cyanic  Acid,  HCNO,  has  to  be  prepared  indirectly. 
When  solid  urea  is  heated  ammonia  is  at  first  evolved,  but 
after  a  time  ceases  ;  if  the  residue  is  dissolved  in  potash 
solution,  addition  of  an  acid  precipitates  Cyanuric  Acid, 
HyC3N3Oy,  which  is  produced  according  to  the  equation  : 

3CON2H4*=H8C8N8O8  +  3NHr 

Urea.  Cyanuric 

acid. 

If  this  cyanuric  acid  is  collected  and  dried,  and  then  heated 
in  a  retort,  vapours  of  cyanic  arid,  HCNO,  are  evolved  : 

H3C3N3O3    =    3HCNO, 
Cyanuric  acid.         Cyanic  acid. 


138  CYANIC  ACID  CHAP,  xx 

and  can  be  condensed  in  a  tube  surrounded  by  a  freezing 
mixture  to  a  very  volatile  liquid,  with  a  marked  and  acrid 
odour.  Cyanic  acid  very  readily  undergoes  polymerisation, 
forming  either  cyanuric  acid  or  another  polymer — cyamelide — 
whose  molecular  formula  is  uncertain. 


QUESTIONS  ON  CHAPTER  XX 

1.  Give  three  methods  by  which  hydrocyanic  acid  can  be  prepared. 

2.  How  would  you  proceed  in  order  to  obtain  mercuric  cyanide  from 
potassium  ferrocyanide  ? 

3  What  happens  when  you  heat  the  following  substances,  (a)  mercuric 
cyanide,  (b)  urea,  (c)  potassium  ferrocyanide? 

4.  What  is  the  composition  of  Prussian  blue?  Describe  its  manu- 
facture. 


I  NDEX 


ACETALDEHYDE,   63 

Alcoholates,  51 

Acetamide,  89 

Alcoholometry,  49 

Acetic  anhydride,  79 

Alcohols,  general  characteristics  of, 

Acetone,  66 

44 

Acetyl  chloride,  79 

Allyl  compounds,  in 

Acetylene,  33 

Amides,  88 

Acid,  acetic,  68,  71 

Amido-acetic  acid,  90 

,,      acrylic,  112 

Amines,  82 

,,      amido-acetic,  90 

,,        primary,    secondary,    and 

,,      butyric,  74,  75 

tertiary,  82,  84,  85 

,,      citric,  1  08 

Argol,  103,  104 

,,      cyanic,  137 

Arsines,  93 

,,      formic,  70 

Asymmetric  carbon  atom,  108 

,,      glycolic,  100 
hydrocyanic,  132 
,,      lactic,  1  06 

BUTANE,  23 
Butylene,  31 

malic,  103 

CACODYL  compounds,  94 

,,      oxalic,  101 

Cane-sugar,  123 

,,      palmitic,  76 

Carbon,  estimation  of,  4 

,  ,      para-lactic,  107 

,,        tetrachloride,  39 

,,      propionic,  74 

Carius's  method  of  analysis,  9 

,,      prussic,  132 

Cellulose,  126 

,,      stearic,  76 

Chloral,  39,  65 

,,      succinic,  102 

Chlorhydrins,   nS 

tartaric,  103 

Chloroform,  38 

,,     uric,  129 
Acrolein,  112,  116 
Alcohol,  allyl,  in 

Couple,  zinc-copper,  20,  95 
Cyanides,  133 
Cyanogen,  131 

amyl,  54 

butyl,  53 

DEXTRIN,  126 

dihydric,  99 

Dextrose,  120 

ethyl,  47,  51 

Dihydric  alcohol,  99 

methyl,  45 

Dulcitol,  120 

,,        primary,    secondary,    and 

Dynamite,  117 

tertiary,  53 

propyl,  52 

ETHANE,  22 

,,        trihydric,  115 

Ether,  58 

140 


ORGANIC  CHEMISTRY 


Ethereal  salts,  55 
Ethyl  acetate,  56 

,,      alcohol,  47,  51 

, ,      bromide,  4 1 

,,      chloride,  40 

,,     ether,  58 

, ,     iodide,  42 

,,      niercaptan,  59 

,,      sulphide,  59 
Ethylamines,  87 
Ethylene,  28 

bromide,  41 

FEHLING'S  solution,  62,  120,  122 
Fermentation,  47 
Formaldehyde,  61 
Formulae,  empirical,  12 
,,         molecular,  13 
Fusel  oil,  47 

GALACTOSE,  121 
Garlic,  oil  of,  113 
Glucose,  119 
Glycerine,  115 
Glycocoll,  90 
Glycol,  99 
Glyoxal,  100 
Gun-cotton,  126 

HALOGENS,  estimation  of,  9 
Hofmann's  method,  15 
Homology,  2,  21 
Hydrogen,  estimation  of,  4 
Hydroxyl  groups,  determination  of, 
80 

INVERT-SUGAR,  124 
lodoform,  39 
Isomerism,  2,  23 

KETONES,  65 

LEAD  ETHYL,  97 
Levulose,  121 

MALTOSE,  124 
Mannitol,  120 
Mercury  methyl,  97 
Methane,  19 
Methyl  alcohol,  45 
,,       chloride,  37 


Methyl  iodide,  39 
Methylamine,  85 
Methylated  spirit,  49 
Milk-sugar,  124 
Mustard,  oil  of,  113 

NITROGEN, 'estimation  of,  6 
Nitro-glycerine,  116 

PARAFFIN,  27 

Paraldehyde,  63 

Pentane,  25 

Petroleum,  26 

Phosphines,  92 

Phosphorus,  estimation  of,  10 

Potassium  ferrocyanide,  135 

Proof  spirit,  50 

Propane,  23 

Propylene,  30 

Prussian  blue,  136 

Pyroxylin,  127 

RAOULT'S  method,  17,  119 

SAPONIFICATION,  57 

Saturated  compounds,  28 

Silicon,  compounds  of,  94 

Soap,  76 

Starch,  125 

Sulphur,  estimation  of,  125 

TARTAR,  cream  of,  104 

,,         emetic,   105 
Tetrahedral    carbon    atom,    theory 

of,  31,  35,  120 
Tin  ethyl,  98 

UNSATURATED  compounds,  28 
Urea,  i,  128 

VAN'T  HOFF'S  theory,  31,  120 
Vapour  density,  14 
Victor  Meyer's  method,  14 

WOOD,  distillation  of,  45 
YEAST,  47 

ZINC  ETHYL,  96 
,,     methyl,  95 


ELEMENTARY  TEXT-BOOKS  ON 
CHEMISTRY. 

PUBLISHED  BY  MACMILLAN  &  CO. 


COHEN.  —  The  Owens  College  Course  of  Practical  Organic 
Chemistry.  By  JULIUS  B.  COHEN,  Ph.D.,  Assistant  Lec- 
turer on  Chemistry  in  the  Owens  College,  Manchester. 
With  a  Preface  by  Sir  HENRY  ROSCOE,  F.R.S.,  and  C. 
SCHORLEMMER,  F.R.S.  i8mo.  70  cents. 

FISHER.  —A  Class-Book  of  Elementary  Chemistry.  With 
60  Illustrations.  I2mo.  $1.10. 

JONES.— The  Owens  College  Junior  Course  of  Practical 
Chemistry.  By  FRANCIS  JONES,  F.R.S.E.,  Chemical 
Master  at  the  Grammar  School,  Manchester.  With  a 
Preface  by  Sir  HENRY  ROSCOE,  F.R.S.  Illustrated. 
i8mo.  70  cents. 

Questions  on  Chemistry.  A  Series  of  Problems  and 
Exercises  in  Inorganic  and  Organic  Chemistry.  By  the 
same  author.  i8mo.  75  cents. 

MUIR  and  CARNEGIE.  — Practical  Chemistry.  A  Course 
of  Laboratory  Work.  With  numerous  Illustrations.  80 
cents. 

MUIR  and  SLATER.  —  Elementary  Chemistry.    $1.25. 

RAMSAY.  —  Experimental  Proofs  of  Chemical  Theory 
for  Beginners.  By  WILLIAM  RAMSAY,  F.R.S.,  Professor 
of  Chemistry  in  University  College,  London.  70  cents. 

ROSCOE.  —  Lessons  in  Elementary  Chemistry,  Inorganic 
and  Organic.  New  Edition,  revised  and  enlarged,  with 
numerous  illustrations.  $1.25. 

THORP  and  TATE.  — A  Series  of  Chemical  Problems. 
With  Key  for  use  in  Colleges  and  Schools.  By  T.  E. 
THORPE,  B.Sc.,  Ph.D.,  F.R.S.  New  Edition,  revised  and 
enlarged  by  W.  TATE.  i6mo.  65  cents. 

WALKER  and  DOBBIN.  —  Chemical  Theory  for  Begin- 
ners. By  JAMES  WALKER,  D.Sc.,  and  LEONARD  DOB- 
BIN, Ph.D.,  Assistants  in  the  Chemistry  Department, 
University  of  Edinburgh.  i6mo.  70  cents. 


MACMILLAN    &   CO., 

66    Fifth  Avenue    -    -    -    New   York. 

i 


MACMILLAN'S 

SCIENCE     CLASS-BOOKS. 

F'cap  Svo. 


LESSONS  IN  APPLIED  MECHANICS.  By  J.  H.  COTTERILL  and  J.  H. 
SLADE.  $1.25. 

"  Undoubtedly  the  best  rudimentary  treatise  on  the  subject  that  has  yet 
appeared."  —  Mechanical  World. 

"  One  of  the  best  little  books  on  the  subject  that  has  come  under  our 
notice  for  some  time." —  Nature. 

"  The  book  is  one  to  be  warmly  recommended."  —  Iron. 

LESSONS  IN  ELEMENTARY  PHYSICS.  By  Professor  BALFOUR  STEW- 
ART, F.R.S.  With  Illustrations  and  Colored  Diagram.  $1.10. 

"  It  is  the  beau  ideal  of  a  scientific  text-book,  clear,  accurate,  and  thor- 
ough, and  withal  written  in  a  style  so  simple  and  interesting  as  to  impart  a 
real  charm  to  the  study."  —  Educational  Times. 

Questions  on  the  Above  for  Schools.    By  T.  H.  CORE.    40  cents. 
EXAMPLES   IN  PHYSICS.     By  Professor  D.  E.  JONES,  B.Sc.     90  cents. 

"  About  sixty  pages  of  new  matter  have  been  added.  .  .  .  The  chief 
merit  of  the  book  is  that  it  supplies  a  complete  and  exhaustive  set  of  prob- 
lems, and  in  the  solution  of  these  pupils  may  be  trained  to  apply  general 
principles."  —  Journal  of  Education. 

"  The  general  arrangement  of  the  book  is  particularly  happy;  it  is  clearly 
the  work  of  a  teacher  whose  object  is  to  increase  the  real  knowledge  of  his 
students,  and  not  merely  to  drive  them  through  the  ordeal  of  an  examina- 
tion." —  Nature. 

ELEMENTARY    LESSONS    IN    ELECTRICITY    AND    MAGNETISM. 

By  Professor  SYLVANUS  P.  THOMPSON.     $1.25. 

"  An  excellent  little  text-book.  .  .  .  The  book  contains  a  large  amount 
of  information,  clearly  stated,  assisted  by  useful  figures,  and  furnished  wilh 
exercises  on  the  twelve  chapters  into  which  it  is  divided.  It  is  a  book  which 
may  be  commended  to  the  beginner  as  an  excellent  introduction  to  the  sub- 
ject."—  Westminster  Review. 

LESSONS   ON  HEAT,  LIGHT,   AND   SOUND.      An   Elementary  Text- 
book.    By  D.  E.  JONES,  B.Sc.     With  Illustrations.     70  cents. 
"  Well  arranged,  clearly  written,  and  contains  many  excellent  problems 
for  testing  the  ability  of  the  pupil  to  apply  the  principles  which  he  is  supposed 
to  have  learned,  .  .  .  and  possesses  that  rarest  of  all  virtues  in  a  school  text- 
book, scientific  accuracy."  —  Educational  Review. 

ELEMENTARY    LESSONS    ON    ASTRONOMY.      By  J.   N.   LOCKYER, 

F.R.S.     With  Illustrations.     $1.25. 

"  It  is  remarkably  clear  and  compact,  the  illustrations  are  also  of  unusual 
excellence.  No  other  book  on  the  subject  that  we  know  is  at  once  so  small 
and  so  good."  —  Guardian. 

"  The  book  is  full,  clear,  sound,  and  worthy  of  attention,  not  only  as  a 
popular  exposition,  but  as  a  scientific  index."  —  Atheneeum. 

Questions  on  the  Above  for  Schools.      By  J.    FORBES-ROBERTSON. 
40  cents. 

LESSONS   IN    ELEMENTARY   CHEMISTRY.     By  Sir  H.  E.  ROSCOE, 

F.R.S.     $1.25. 

"Much  new  matter  has  been  added  to  keep  the  book  up  to  date.  We 
have  always  considered  it  the  best  work  for  those  who  wish  to  get  a  clear  and 
connected  knowledge  of  the  outlines  of  Inorganic  and  Organic  Chemistry." 
—  Journal  of  Education. 


SCIENCE    CLASS-BOOKS. 


"  It  still  holds  its  position  among  the  very  best  text-books  of  elementary 
chemistry." —  School  Board  Chronicle. 

Problems  adapted  to  the  Above.     By  Professor  THORPE  and  W.  TATE. 
With  Key.     65  cents. 

INORGANIC  CHEMISTRY  FOR  BEGINNERS.  By  Sir  HENRY  ROSCOE, 
F.R.S.,  assisted  by  JOSEPH  LUNT,  F.C.S.  75  cents. 

OWENS  COLLEGE  JUNIOR  COURSE  OF  PRACTICAL  CHEMISTRY. 

By  F.  JONES.  With  Preface  by  Sir  H.  ROSCOE,  F.R.S.  70  cents. 
"  It  is  eminently  practical.  The  text  is  concise,  and  at  the  same  time  accu- 
rate. The  instructions  concerning  experiments  are  clear,  and  calculated  to 
develop  observant  habits.  At  the  end  of  the  book  there  are  some  well  se- 
lected questions,  which  should  ensure  a  thorough  understanding  of  the  facts 
to  which  they  refer."  —  Chemist  and  Druggist. 

OWENS   COLLEGE   COURSE    OF    PRACTICAL   ORGANIC    CHEMIS- 
TRY.     By  JULIUS  B.  COHEN,  Ph.D.      With  Preface  by  Sir  H.  E. 
ROSCOE  and  Professor  SCHORLEMMER.     70  cents. 
"  It  is  with  great  pleasure  that  we  announce  the  appearance  of  this  useful 

little  work,  in  which  the  author  has  cut  out  a  new  patli  of  his  own,  by  the 

exclusively   practical   character   of  the   lessons   and   by  the   style    he    has 

adopted."  —  Chemical  Trade  Journal. 

CHEMICAL  THEORY  FOR  BEGINNERS.  By  L.  DOBBIN,  Ph.D.,  and 
J.  WALKER,  Ph.D.  70  cents. 

"  This  excellent  and  useful  little  work  conducts  the  beginner  over  the 
early  stages  of  his  journey  and  securely  grounds  him  in  chemical  theory." — 
Scotsman. 

"  Elementary  students  are  told  just  sufficient  to  enable  them  to  work  out 
a  chemical  problem.  This  book  is  intended  to  come  to  the  help  of  the  stu- 
dent in  his  transition  stage,  and  contains  an  exceptionally  clear  concise 
explanation  of  chemical  theory."  —  Journal  of  Education. 

LESSONS  IN  ELEMENTARY  PHYSIOLOGY.  By  Rt.  Hon.  T.  H. 
HUXLEY,  F.R.S.  $1.10. 

"It  is  an  admirable  illustration  of  how  the  greatest  master  of  a  science 
may  teach  its  elements  in  the  most  simple  manner."  —  Medical  Press. 

"  A  very  useful  little  manual,  which  should  be  received  with  acclama- 
tion." —  Spectator. 

Questions  on  the  Above  for  Schools.     By  ALCOCK.    40  cents. 
LESSONS  IN  ELEMENTARY  ANATOMY.     By  ST.  G.  MIVART,  F.R.S. 
$1-75- 

"  It  may  be  questioned  whether  any  other  work  on  anatomy  contains  in 
like  compass  so  proportionately  great  a  mass  of  information." —  Lancet. 

"  Its  utility  to  the  general  reader  who  desires,  in  a  small  space,  to  be 
acquainted  with  the  leading  facts  and  generalizations  of  modern  comparative 
anatomy  is  manifest."  —  Pall  Mall  Gazette. 

ELEMENTARY    LESSONS    IN    PHYSICAL    GEOGRAPHY.       By    Sir 

ARCHIBALD  GEIKIE,  F.R.S.     Illustrated.     $1.10. 

"  The  language  is  always  simple  and  clear,  and  the  descriptions  of  the 
various  phenomena  are  no  less  vivid  than  interesting:  the  lessons  are  never 
dull,  never  wearisome,  and  they  can  scarcely  fail  to  make  the  study  of  Phys- 
ical Geography  popular  wherever  they  are  used."  —  Academy. 

Questions  on  the  Same  for  Schools.    i8mo.    40  cents. 


MACMILLAN    &   CO., 

66  Fifth  Avenue    -    -    -    New  York. 


MACMILLAN'S    BOOKS  ON 

ELEMENTARY     SCIENCE. 


AWDRY  (MRS.  W.).  —  Easy  Lessons  on  Light.  Illustrated.  i6mo. 
70  cents. 

BARNETT  (E.  A.)  and  O'NEIL  (H.  C.).  — Primer  of  Domestic  Econ- 
omy. i8mo.  35  cents. 

BARTHOLOMEW.  —  Elementary  School  Atlas.  Colored  Maps  and 
Plans.  30  cents. 

BERNERS  (J.).— First  Lessons  in  Health.     i8mo.     30  cents. 

BETTANY  (G.  T.).— First  Lessons  in  Practical  Botany.  i8mo.  30 
cents. 

C  ANNAN. —Elementary  Political  Economy.    i6mo.    ascents. 

DAWSON  and  SUTHERLAND. —  Geography  of  the  British  Colonies. 
Illustrated.  i6mo.  80  cents. 

DURHAM.  —Science  in  Plain  Language:  — 
Evolution,  Antiquity  of  Man,  etc.     50  cents. 
Astronomy,  etc.    50  cents. 
Food.     50  cents. 

GEIKIE. —Elementary  Geography  of  the  British  Isles.  i8mo.  30 
cents. 

HOROBIN  (J.  C.)-  — Elementary  Mechanics.  Stage  I.  With  numerous 
Illustrations.  i6mo.  50  cents. 

JEVONS  (W.  S.).  —  Elementary  Lessons  in  Logic.    i8mo.    40  cents. 

LAURIE  (A.  P.).  — The  Food  of  Plants.  An  Introduction  to  Agricul- 
tural Chemistry.  With  Illustrations.  i8mo.  35  cents. 

LOCK. — Mechanics  for  Beginners.  Part  I.  Dynamics  and  Statics. 
i6mo.  90  cents. 

LOEWY. —Experimental  Physics.    F'cap  8vo.    50  cents. 

A  Graduated  Course  of  Natural  Science.  Part  I.  First  Year's  Course. 
i6mo.  60  cents.  Part  II.  Second  and  Third  Years'  Course.  i6mo. 
60  cents. 

MARTINEAU  (C.  A.).  — Easy  Lessons  on  Heat.  Illustrated.  i6mo. 
70  cents. 

MAYCOCK  (W.  P.).  — A  First  Book  of  Electricity  and  Magnetism. 
60  cents. 

MILL  (H.  R.).  —Elementary  Commercial  Geography.    i6mo.    30  cents. 

PILLANS  (PROFESSOR).  — First  Steps  in  Physical  and  Classical  Geog- 
raphy. i4th  Edition.  Illustrated  with  Maps.  By  THOMAS  FAW- 
CETT.  i6mo.  50  cents. 

TANNER.  —  First  Principles  of  Agriculture.     i8mo.     30  cents. 

WRIGHT.  —  Horticulture.  Ten  Lectures  delivered  for  the  Surrey  County 
Council.  i8mo.  35  cents. 


MACMILLAN    &    CO., 

66    Fifth  Avenue    -    -    -    New  York. 

8 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
This  book  is  DUE  on  the  last  date  stamped  below. 


OCT   17  1947 


NOV    5   1947 


2  v  (956 


NOV  14  1958  L 


ij 


REC'D  LD 

APR  12  1961 


LD  21-100m-12,'46(A2012sl6)4120 


889778 

§ -2  £3 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


